diff --git a/src/main/java/com/onixbyte/deltaforceguide/DeltaForceGuideApplication.java b/src/main/java/com/onixbyte/deltaforceguide/DeltaForceGuideApplication.java
index 4d69512..a23fb88 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/DeltaForceGuideApplication.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/DeltaForceGuideApplication.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 
+/**
+ * Entry point for the Delta Force Guide Server application.
+ *
+ * @author zihluwang
+ */
 @SpringBootApplication
 public class DeltaForceGuideApplication {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/client/TokenClient.java b/src/main/java/com/onixbyte/deltaforceguide/client/TokenClient.java
index d4b745c..a7ad3f1 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/client/TokenClient.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/client/TokenClient.java
@@ -12,6 +12,11 @@ import org.springframework.stereotype.Component;
 
 import java.time.LocalDateTime;
 
+/**
+ * Client for generating and verifying JSON Web Tokens using the Auth0 java-jwt library.
+ *
+ * @author zihluwang
+ */
 @Component
 public class TokenClient {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/config/CorsConfig.java b/src/main/java/com/onixbyte/deltaforceguide/config/CorsConfig.java
index 291695b..1e13243 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/config/CorsConfig.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/config/CorsConfig.java
@@ -12,10 +12,21 @@ import org.springframework.web.cors.UrlBasedCorsConfigurationSource;
 import java.util.List;
 import java.util.stream.Stream;
 
+/**
+ * Configuration for CORS (Cross-Origin Resource Sharing) policies.
+ *
+ * @author zihluwang
+ */
 @Configuration
 @EnableConfigurationProperties({CorsProperties.class})
 public class CorsConfig {
 
+    /**
+     * Creates the CORS configuration source with properties from configuration.
+     *
+     * @param properties the CORS configuration properties
+     * @return the CORS configuration source
+     */
     @Bean
     public CorsConfigurationSource corsConfigurationSource(
             CorsProperties properties
diff --git a/src/main/java/com/onixbyte/deltaforceguide/config/JacksonConfig.java b/src/main/java/com/onixbyte/deltaforceguide/config/JacksonConfig.java
index a64a1ea..895bcd1 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/config/JacksonConfig.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/config/JacksonConfig.java
@@ -6,6 +6,11 @@ import org.springframework.boot.autoconfigure.jackson.Jackson2ObjectMapperBuilde
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
+/**
+ * Configuration for Jackson JSON serialisation and deserialisation settings.
+ *
+ * @author zihluwang
+ */
 @Configuration
 public class JacksonConfig {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/config/MyBatisConfig.java b/src/main/java/com/onixbyte/deltaforceguide/config/MyBatisConfig.java
index 61acbfc..0e2ae74 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/config/MyBatisConfig.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/config/MyBatisConfig.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.config;
 import org.mybatis.spring.annotation.MapperScan;
 import org.springframework.context.annotation.Configuration;
 
+/**
+ * Configuration for MyBatis SQL mapping framework integration.
+ *
+ * @author zihluwang
+ */
 @Configuration
 @MapperScan(basePackages = {"com.onixbyte.deltaforceguide.mapper"})
 public class MyBatisConfig {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/config/SecurityConfig.java b/src/main/java/com/onixbyte/deltaforceguide/config/SecurityConfig.java
index 8e8cc50..b32a691 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/config/SecurityConfig.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/config/SecurityConfig.java
@@ -23,12 +23,23 @@ import org.springframework.security.web.SecurityFilterChain;
 import org.springframework.security.web.access.ExceptionTranslationFilter;
 import org.springframework.web.cors.CorsConfigurationSource;
 
+/**
+ * Spring Security configuration defining authentication, authorisation, and filter chains.
+ *
+ * @author zihluwang
+ */
 @Configuration
 @EnableWebSecurity
 @EnableMethodSecurity
 @EnableConfigurationProperties({TokenProperties.class, CookieProperties.class})
 public class SecurityConfig {
 
+    /**
+     * Configures the HTTP security filter chain including endpoint authorisation and JWT filter.
+     *
+     * @param http the HTTP security builder
+     * @return the configured security filter chain
+     */
     @Bean
     public SecurityFilterChain securityFilterChain(
             HttpSecurity httpSecurity,
@@ -48,11 +59,20 @@ public class SecurityConfig {
                 .build();
     }
 
+    /**
+     * Provides the BCrypt password encoder for credential hashing.
+     * @return the BCrypt password encoder
+     */
     @Bean
     public PasswordEncoder passwordEncoder() {
         return new BCryptPasswordEncoder();
     }
 
+    /**
+     * Provides the authentication manager for the security configuration.
+     *
+     * @return the authentication manager
+     */
     @Bean
     public AuthenticationManager authenticationManager(
             UsernamePasswordAuthenticationProvider usernamePasswordAuthenticationProvider
diff --git a/src/main/java/com/onixbyte/deltaforceguide/config/SpringDataConfig.java b/src/main/java/com/onixbyte/deltaforceguide/config/SpringDataConfig.java
index 44e3a4c..1dfe3ff 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/config/SpringDataConfig.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/config/SpringDataConfig.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.config;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
 
+/**
+ * Configuration for Spring Data JPA auditing and repository settings.
+ *
+ * @author zihluwang
+ */
 @Configuration
 @EnableJpaRepositories(basePackages = {"com.onixbyte.deltaforceguide.repository"})
 public class SpringDataConfig {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/AuthController.java b/src/main/java/com/onixbyte/deltaforceguide/controller/AuthController.java
index 86229aa..0a42067 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/AuthController.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/AuthController.java
@@ -19,6 +19,11 @@ import org.springframework.web.bind.annotation.RestController;
 
 import java.time.Duration;
 
+/**
+ * REST controller for user authentication endpoints (login, logout).
+ *
+ * @author zihluwang
+ */
 @Tag(name = "用户鉴权", description = "处理用户登录与退出功能")
 @RestController
 @RequestMapping("/auth")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/DailyPasswordController.java b/src/main/java/com/onixbyte/deltaforceguide/controller/DailyPasswordController.java
index f817f66..527e730 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/DailyPasswordController.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/DailyPasswordController.java
@@ -8,6 +8,11 @@ import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RestController;
 
+/**
+ * REST controller for retrieving daily-generated passwords.
+ *
+ * @author zihluwang
+ */
 @Tag(name = "每日密码", description = "获取每日密码信息")
 @RestController
 @RequestMapping("/daily-passwords")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/FirearmController.java b/src/main/java/com/onixbyte/deltaforceguide/controller/FirearmController.java
index 7d95b69..4843c2d 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/FirearmController.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/FirearmController.java
@@ -15,6 +15,11 @@ import org.springframework.data.domain.Sort;
 import org.springframework.validation.annotation.Validated;
 import org.springframework.web.bind.annotation.*;
 
+/**
+ * REST controller for firearm CRUD operations.
+ *
+ * @author zihluwang
+ */
 @Tag(name = "武器管理", description = "与武器有关的操作")
 @RestController
 @RequestMapping("/firearms")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/GlobalExceptionHandler.java b/src/main/java/com/onixbyte/deltaforceguide/controller/GlobalExceptionHandler.java
index c0b19f1..4edd154 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/GlobalExceptionHandler.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/GlobalExceptionHandler.java
@@ -6,6 +6,11 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
 
+/**
+ * Global exception handler that translates exceptions into standard error responses.
+ *
+ * @author zihluwang
+ */
 @RestControllerAdvice
 public class GlobalExceptionHandler {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/ModificationController.java b/src/main/java/com/onixbyte/deltaforceguide/controller/ModificationController.java
index b7c7a8d..7eaf94c 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/ModificationController.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/ModificationController.java
@@ -27,6 +27,11 @@ import org.springframework.web.bind.annotation.RestController;
 
 import java.util.List;
 
+/**
+ * REST controller for modification CRUD operations, including batch creation and deletion.
+ *
+ * @author zihluwang
+ */
 @Tag(name = "改装管理", description = "对枪械改装的管理")
 @RestController
 @RequestMapping("/modifications")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/controller/TagController.java b/src/main/java/com/onixbyte/deltaforceguide/controller/TagController.java
index e22097d..b9f4e59 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/controller/TagController.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/controller/TagController.java
@@ -10,6 +10,11 @@ import com.onixbyte.deltaforceguide.service.ModificationService;
 
 import java.util.List;
 
+/**
+ * REST controller for retrieving available modification tags.
+ *
+ * @author zihluwang
+ */
 @Tag(name = "标签管理", description = "管理标签信息")
 @RestController
 @RequestMapping("/tags")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/converter/FirearmTypeConverter.java b/src/main/java/com/onixbyte/deltaforceguide/domain/converter/FirearmTypeConverter.java
index f6f46f8..8108db3 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/converter/FirearmTypeConverter.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/converter/FirearmTypeConverter.java
@@ -4,6 +4,11 @@ import com.onixbyte.deltaforceguide.enumeration.FirearmType;
 import jakarta.persistence.AttributeConverter;
 import jakarta.persistence.Converter;
 
+/**
+ * JPA attribute converter that maps {@link FirearmType} enum to/from its integer database representation.
+ *
+ * @author zihluwang
+ */
 @Converter
 public class FirearmTypeConverter implements AttributeConverter<FirearmType, Integer> {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryRequest.java
index 29fa638..b94b61c 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryRequest.java
@@ -6,6 +6,11 @@ import jakarta.validation.constraints.NotBlank;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Request DTO for creating or updating an accessory attached to a modification.
+ *
+ * @author zihluwang
+ */
 public record AccessoryRequest(
         @NotBlank(message = "插槽名称不能为空")
         String slotName,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryResponse.java
index 421410d..ade3eac 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/AccessoryResponse.java
@@ -4,6 +4,11 @@ import com.onixbyte.deltaforceguide.domain.entity.Accessory;
 
 import java.util.List;
 
+/**
+ * Response DTO for an accessory attached to a modification.
+ *
+ * @author zihluwang
+ */
 public record AccessoryResponse(
         String slotName,
         String accessoryName,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPassword.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPassword.java
index 2a381ad..edfa9c0 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPassword.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPassword.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+/**
+ * DTO representing a single daily-generated password for a map.
+ *
+ * @author zihluwang
+ */
 public record DailyPassword(
         String mapName,
         String password
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordData.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordData.java
index c685542..5e3c12f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordData.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordData.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 import java.time.LocalDateTime;
 import java.util.List;
 
+/**
+ * DTO containing daily password data including update information and password list.
+ *
+ * @author zihluwang
+ */
 public record DailyPasswordData(
         String updateDate,
         Integer totalCount,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordMetadata.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordMetadata.java
index a2fa36b..9af994f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordMetadata.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordMetadata.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+/**
+ * DTO holding metadata about the daily password source and update tracking.
+ *
+ * @author zihluwang
+ */
 public record DailyPasswordMetadata(
         String version,
         String author
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordResponse.java
index 7d29a27..d3ce808 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/DailyPasswordResponse.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+/**
+ * Response DTO wrapping daily password data with metadata.
+ *
+ * @author zihluwang
+ */
 public record DailyPasswordResponse(
         String status,
         String message,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ErrorResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ErrorResponse.java
index f1efbfa..11879fc 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ErrorResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ErrorResponse.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.domain.dto;
 
+/**
+ * Standard error response body returned on API failures.
+ *
+ * @author zihluwang
+ */
 public record ErrorResponse(
         String message
 ) {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmRequest.java
index 74e1993..02fb855 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmRequest.java
@@ -2,6 +2,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 
 import com.onixbyte.deltaforceguide.enumeration.FirearmType;
 
+/**
+ * Request DTO for creating or updating a firearm.
+ *
+ * @author zihluwang
+ */
 public record FirearmRequest(
         String name,
         FirearmType type,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmResponse.java
index eb5b1ac..0e9eaba 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/FirearmResponse.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 import com.onixbyte.deltaforceguide.domain.entity.Firearm;
 import com.onixbyte.deltaforceguide.enumeration.FirearmType;
 
+/**
+ * Response DTO for a firearm record, including associated modifications.
+ *
+ * @author zihluwang
+ */
 public record FirearmResponse(
         Long id,
         String name,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/LoginRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/LoginRequest.java
index ab820ec..106d533 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/LoginRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/LoginRequest.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 import io.swagger.v3.oas.annotations.media.Schema;
 import jakarta.validation.constraints.NotBlank;
 
+/**
+ * Login request containing principle (username/email) and credential (password).
+ *
+ * @author zihluwang
+ */
 @Schema(description = "登录请求")
 public record LoginRequest(
         @NotBlank(message = "登录名称不能为空")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchCreateRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchCreateRequest.java
index cdb3d93..c0aa59f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchCreateRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchCreateRequest.java
@@ -5,6 +5,11 @@ import jakarta.validation.constraints.NotEmpty;
 
 import java.util.List;
 
+/**
+ * Request DTO for batch creation of modifications.
+ *
+ * @author zihluwang
+ */
 public record ModificationBatchCreateRequest(
         @NotEmpty(message = "批量创建列表不能为空")
         List<@Valid ModificationRequest> modifications
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchDeleteRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchDeleteRequest.java
index 7e46400..4243895 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchDeleteRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationBatchDeleteRequest.java
@@ -5,6 +5,11 @@ import jakarta.validation.constraints.Positive;
 
 import java.util.List;
 
+/**
+ * Request DTO for batch deletion of modifications by ID.
+ *
+ * @author zihluwang
+ */
 public record ModificationBatchDeleteRequest(
         @NotEmpty(message = "批量删除ID列表不能为空")
         List<@Positive(message = "ID必须为正数") Long> ids
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationRequest.java
index c602dbd..e4f6708 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationRequest.java
@@ -8,6 +8,11 @@ import jakarta.validation.constraints.Positive;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Request DTO for creating or updating a modification.
+ *
+ * @author zihluwang
+ */
 public record ModificationRequest(
         @NotNull(message = "武器ID不能为空")
         @Positive(message = "武器ID必须为正数")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationResponse.java
index c4d4492..aca6ef5 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/ModificationResponse.java
@@ -4,6 +4,11 @@ import com.onixbyte.deltaforceguide.domain.entity.Modification;
 
 import java.util.List;
 
+/**
+ * Response DTO for a modification record including accessories and tags.
+ *
+ * @author zihluwang
+ */
 public record ModificationResponse(
         Long id,
         Long firearmId,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/PageResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/PageResponse.java
index 0eefb62..20738bd 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/PageResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/PageResponse.java
@@ -4,6 +4,11 @@ import org.springframework.data.domain.Page;
 
 import java.util.List;
 
+/**
+ * Generic paginated response wrapper for list endpoints.
+ *
+ * @author zihluwang
+ */
 public record PageResponse<T>(
         List<T> items,
         int page,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningRequest.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningRequest.java
index 414becd..a180eb3 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningRequest.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningRequest.java
@@ -3,6 +3,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 import jakarta.validation.constraints.NotBlank;
 import jakarta.validation.constraints.NotNull;
 
+/**
+ * Request DTO for a tuning adjustment on an accessory.
+ *
+ * @author zihluwang
+ */
 public record TuningRequest(
         @NotBlank(message = "调校项名称不能为空")
         String tuningName,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningResponse.java
index 3f6febf..405ecde 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/TuningResponse.java
@@ -2,6 +2,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 
 import com.onixbyte.deltaforceguide.domain.entity.Tuning;
 
+/**
+ * Response DTO for a tuning adjustment on an accessory.
+ *
+ * @author zihluwang
+ */
 public record TuningResponse(
         String tuningName,
         Double tuningValue
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/UserResponse.java b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/UserResponse.java
index 75d9188..b20231b 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/dto/UserResponse.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/dto/UserResponse.java
@@ -2,6 +2,11 @@ package com.onixbyte.deltaforceguide.domain.dto;
 
 import com.onixbyte.deltaforceguide.domain.entity.User;
 
+/**
+ * Response DTO for a user account, including associated credentials.
+ *
+ * @author zihluwang
+ */
 public record UserResponse(
         Long id,
         String username,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Accessory.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Accessory.java
index b76b622..cde914d 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Accessory.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Accessory.java
@@ -4,6 +4,11 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
 
+/**
+ * Entity representing an accessory attached to a modification, stored as JSONB.
+ *
+ * @author zihluwang
+ */
 public class Accessory {
 
     private String slotName;
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Firearm.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Firearm.java
index 65942d3..c71cee7 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Firearm.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Firearm.java
@@ -15,6 +15,11 @@ import jakarta.persistence.Table;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Entity representing a firearm in the Delta Force game.
+ *
+ * @author zihluwang
+ */
 @Entity
 @Table(name = "firearm")
 public class Firearm {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Modification.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Modification.java
index ed145b5..a1942f7 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Modification.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Modification.java
@@ -7,6 +7,11 @@ import org.hibernate.annotations.Type;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Entity representing a firearm modification or build configuration.
+ *
+ * @author zihluwang
+ */
 @Entity
 @Table(
     name = "modification",
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Tuning.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Tuning.java
index 83eb1b8..a4eb1f1 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Tuning.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/Tuning.java
@@ -2,6 +2,11 @@ package com.onixbyte.deltaforceguide.domain.entity;
 
 import java.util.Objects;
 
+/**
+ * Entity representing a tuning adjustment for an accessory, stored as JSONB within Accessory.
+ *
+ * @author zihluwang
+ */
 public class Tuning {
 
     private String tuningName;
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/User.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/User.java
index 67142df..d696b2d 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/User.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/User.java
@@ -12,6 +12,11 @@ import jakarta.persistence.Table;
 import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Entity representing an application user with authentication credentials.
+ *
+ * @author zihluwang
+ */
 @Entity
 @Table(name = "app_user")
 public class User {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredential.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredential.java
index b8a09a6..2ecdd37 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredential.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredential.java
@@ -12,6 +12,11 @@ import jakarta.persistence.MapsId;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.Table;
 
+/**
+ * Entity representing a user credential linked to an authentication provider.
+ *
+ * @author zihluwang
+ */
 @Entity
 @Table(name = "app_user_credential")
 public class UserCredential {
@@ -28,7 +33,7 @@ public class UserCredential {
 	@JoinColumn(name = "user_id", nullable = false, foreignKey = @ForeignKey(name = "fk_user_credential_user"))
 	private User user;
 
-	@Column(name = "credential", nullable = false, length = 255)
+	@Column(name = "credential", nullable = false)
 	private String credential;
 
 	public UserCredentialId getId() {
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredentialId.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredentialId.java
index 57a819e..1e25f45 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredentialId.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/UserCredentialId.java
@@ -5,6 +5,11 @@ import jakarta.persistence.Embeddable;
 import java.io.Serializable;
 import java.util.Objects;
 
+/**
+ * Composite key for the UserCredential entity, combining user ID and provider.
+ *
+ * @author zihluwang
+ */
 @Embeddable
 public class UserCredentialId implements Serializable {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/enumeration/FirearmType.java b/src/main/java/com/onixbyte/deltaforceguide/enumeration/FirearmType.java
index d4965fa..77bdbdb 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/enumeration/FirearmType.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/enumeration/FirearmType.java
@@ -1,5 +1,11 @@
 package com.onixbyte.deltaforceguide.enumeration;
 
+/**
+ * Enumeration of firearm types in the Delta Force game.
+ * Each type is associated with an integer code used for database persistence.
+ *
+ * @author zihluwang
+ */
 public enum FirearmType {
 
     RIFLE(0),
@@ -21,6 +27,13 @@ public enum FirearmType {
         return code;
     }
 
+    /**
+     * Resolve a FirearmType from its integer code.
+     *
+      * @param code the integer code, may be null
+     * @return the corresponding FirearmType, or null if the code is null
+     * @throws IllegalArgumentException if the code does not match any known type
+     */
     public static FirearmType fromCode(Integer code) {
         if (code == null) {
             return null;
diff --git a/src/main/java/com/onixbyte/deltaforceguide/exeption/BizException.java b/src/main/java/com/onixbyte/deltaforceguide/exeption/BizException.java
index aad96d2..d1b7ff2 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/exeption/BizException.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/exeption/BizException.java
@@ -2,6 +2,11 @@ package com.onixbyte.deltaforceguide.exeption;
 
 import org.springframework.http.HttpStatus;
 
+/**
+ * Custom runtime exception that carries an HTTP status code for API error responses.
+ *
+ * @author zihluwang
+ */
 public class BizException extends RuntimeException {
 
     /**
diff --git a/src/main/java/com/onixbyte/deltaforceguide/filter/TokenAuthenticationFilter.java b/src/main/java/com/onixbyte/deltaforceguide/filter/TokenAuthenticationFilter.java
index f4b9220..e2068a6 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/filter/TokenAuthenticationFilter.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/filter/TokenAuthenticationFilter.java
@@ -16,7 +16,6 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
-import org.springframework.security.core.GrantedAuthority;
 import org.springframework.security.core.context.SecurityContextHolder;
 import org.springframework.stereotype.Component;
 import org.springframework.web.filter.OncePerRequestFilter;
@@ -29,6 +28,11 @@ import java.time.Instant;
 import java.util.Objects;
 import java.util.Optional;
 
+/**
+ * Servlet filter that extracts and validates JWT tokens from httpOnly cookies for each request.
+ *
+ * @author zihluwang
+ */
 @Component
 public class TokenAuthenticationFilter extends OncePerRequestFilter {
 
@@ -52,6 +56,13 @@ public class TokenAuthenticationFilter extends OncePerRequestFilter {
         this.handlerExceptionResolver = handlerExceptionResolver;
     }
 
+    /**
+     * Extracts JWT from httpOnly cookie, validates it, and sets the security context.
+     *
+     * @param request the HTTP request
+     * @param response the HTTP response
+     * @param filterChain the filter chain
+     */
     @Override
     protected void doFilterInternal(
             @NonNull HttpServletRequest request,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/manager/CookieManager.java b/src/main/java/com/onixbyte/deltaforceguide/manager/CookieManager.java
index 7bec528..f6ef16f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/manager/CookieManager.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/manager/CookieManager.java
@@ -6,6 +6,11 @@ import org.springframework.stereotype.Component;
 
 import java.time.Duration;
 
+/**
+ * Manager providing cookie construction operations with configurable properties.
+ *
+ * @author zihluwang
+ */
 @Component
 public class CookieManager {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/manager/DailyPasswordManager.java b/src/main/java/com/onixbyte/deltaforceguide/manager/DailyPasswordManager.java
index 3ec28f9..6b6ac59 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/manager/DailyPasswordManager.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/manager/DailyPasswordManager.java
@@ -17,6 +17,11 @@ import java.time.Duration;
 import java.time.LocalDate;
 import java.util.Objects;
 
+/**
+ * Manager for daily password data access and caching coordination.
+ *
+ * @author zihluwang
+ */
 @Component
 public class DailyPasswordManager {
 
@@ -49,6 +54,10 @@ public class DailyPasswordManager {
         this.redisTemplate = redisTemplate;
     }
 
+    /**
+     * Retrieves the daily password from cache or generates a new one.
+     * @return the daily password response
+     */
     public DailyPasswordResponse getDailyPassword() {
         var key = CACHE_KEY_PREFIX + LocalDate.now();
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/manager/UserCredentialManager.java b/src/main/java/com/onixbyte/deltaforceguide/manager/UserCredentialManager.java
index f4aa494..d77c687 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/manager/UserCredentialManager.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/manager/UserCredentialManager.java
@@ -3,11 +3,15 @@ package com.onixbyte.deltaforceguide.manager;
 import com.onixbyte.deltaforceguide.domain.entity.UserCredential;
 import com.onixbyte.deltaforceguide.repository.UserCredentialRepository;
 import org.springframework.stereotype.Component;
-import org.springframework.transaction.annotation.Transactional;
 
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Manager for user credential persistence and authentication data access.
+ *
+ * @author zihluwang
+ */
 @Component
 public class UserCredentialManager {
 
@@ -17,27 +21,52 @@ public class UserCredentialManager {
         this.userCredentialRepository = userCredentialRepository;
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds all credentials belonging to a specific user.
+     *
+     * @param userId the user ID
+     * @return list of matching credentials
+     */
     public List<UserCredential> findAllByUserId(Long userId) {
         return userCredentialRepository.findAllByUserId(userId);
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a credential for a specific user and provider combination.
+     *
+     * @param userId the user ID
+     * @param provider the authentication provider
+     * @return the matching credential, if found
+     */
     public Optional<UserCredential> findByUserIdAndProvider(Long userId, String provider) {
         return userCredentialRepository.findByUserIdAndProvider(userId, provider);
     }
 
-    @Transactional
+    /**
+     * Persists a new or updated credential.
+     *
+     * @param userCredential the credential to save
+     * @return the saved credential
+     */
     public UserCredential save(UserCredential userCredential) {
         return userCredentialRepository.save(userCredential);
     }
 
-    @Transactional
+    /**
+     * Deletes a credential for a specific user and provider.
+     *
+     * @param userId the user ID
+     * @param provider the authentication provider
+     */
     public void deleteByUserIdAndProvider(Long userId, String provider) {
         userCredentialRepository.deleteByUserIdAndProvider(userId, provider);
     }
 
-    @Transactional
+    /**
+     * Deletes all credentials belonging to a user.
+     *
+     * @param userId the user ID
+     */
     public void deleteAllByUserId(Long userId) {
         userCredentialRepository.deleteAllByUserId(userId);
     }
diff --git a/src/main/java/com/onixbyte/deltaforceguide/manager/UserManager.java b/src/main/java/com/onixbyte/deltaforceguide/manager/UserManager.java
index fb8ac56..d63c0f7 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/manager/UserManager.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/manager/UserManager.java
@@ -8,6 +8,11 @@ import org.springframework.transaction.annotation.Transactional;
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Manager for user entity persistence and query operations.
+ *
+ * @author zihluwang
+ */
 @Component
 public class UserManager {
 
@@ -17,17 +22,30 @@ public class UserManager {
         this.userRepository = userRepository;
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a user by their ID.
+     *
+     * @param id the user ID
+     * @return the matching user, if found
+     */
     public Optional<User> findById(Long id) {
         return userRepository.findById(id);
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Retrieves all registered users.
+     * @return list of all users
+     */
     public List<User> findAll() {
         return userRepository.findAll();
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a user by their username.
+     *
+     * @param username the username to search for
+     * @return the matching user, if found
+     */
     public Optional<User> findByUsername(String username) {
         return userRepository.findByUsername(username);
     }
@@ -37,16 +55,31 @@ public class UserManager {
         return userRepository.findByEmail(email);
     }
 
-    @Transactional
+    /**
+     * Persists a new or updated user.
+     *
+     * @param user the user to save
+     * @return the saved user
+     */
     public User save(User user) {
         return userRepository.save(user);
     }
 
-    @Transactional
+    /**
+     * Deletes a user by their ID.
+     *
+     * @param id the user ID to delete
+     */
     public void deleteById(Long id) {
         userRepository.deleteById(id);
     }
 
+    /**
+     * Finds a user by their username or email address.
+     *
+     * @param principal the username or email to search for
+     * @return the matching user, if found
+     */
     public Optional<User> findByUsernameOrEmail(String principal) {
         return userRepository.findByUsernameOrEmail(principal);
     }
diff --git a/src/main/java/com/onixbyte/deltaforceguide/properties/CookieProperties.java b/src/main/java/com/onixbyte/deltaforceguide/properties/CookieProperties.java
index 86dab77..0cfde08 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/properties/CookieProperties.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/properties/CookieProperties.java
@@ -6,6 +6,16 @@ import org.springframework.boot.web.server.Cookie;
 
 import java.time.Duration;
 
+/**
+ * Configuration properties for HTTP cookies used in authentication, prefixed with "app.cookie".
+ *
+ * @param httpOnly  whether the cookie is httpOnly
+ * @param secure    whether the cookie is secure
+ * @param path      the cookie path
+ * @param maxAge    the maximum age of the cookie
+ * @param sameSite  the SameSite policy for the cookie
+ * @author zihluwang
+ */
 @ConfigurationProperties(prefix = "app.cookie")
 public record CookieProperties(
         @DefaultValue("true") Boolean httpOnly,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/properties/CorsProperties.java b/src/main/java/com/onixbyte/deltaforceguide/properties/CorsProperties.java
index ff064d5..193640f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/properties/CorsProperties.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/properties/CorsProperties.java
@@ -6,6 +6,18 @@ import org.springframework.http.HttpMethod;
 
 import java.time.Duration;
 
+/**
+ * Configuration properties for CORS settings, prefixed with "app.cors".
+ *
+ * @param allowedHeaders      headers allowed in CORS requests
+ * @param allowedMethods      HTTP methods allowed in CORS requests
+ * @param allowedOrigins      origins permitted to make cross-origin requests
+ * @param allowCredentials    whether credentials are allowed in CORS requests
+ * @param allowPrivateNetwork whether private network access is permitted
+ * @param maxAge              how long the CORS preflight response may be cached
+ * @param exposedHeaders      headers exposed to the client in CORS responses
+ * @author zihluwang
+ */
 @ConfigurationProperties(prefix = "app.cors")
 public record CorsProperties(
         @DefaultValue({"Content-Type", "Authorization"})
diff --git a/src/main/java/com/onixbyte/deltaforceguide/properties/TokenProperties.java b/src/main/java/com/onixbyte/deltaforceguide/properties/TokenProperties.java
index 0d7a618..74c693c 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/properties/TokenProperties.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/properties/TokenProperties.java
@@ -4,6 +4,14 @@ import org.springframework.boot.context.properties.ConfigurationProperties;
 
 import java.time.Duration;
 
+/**
+ * Configuration properties for JWT token generation and validation, prefixed with "app.jwt".
+ *
+ * @param issuer    the JWT issuer claim
+ * @param secret    the signing secret for JWT tokens
+ * @param validTime the duration for which a token remains valid
+ * @author zihluwang
+ */
 @ConfigurationProperties(prefix = "app.jwt")
 public record TokenProperties(
         String issuer,
diff --git a/src/main/java/com/onixbyte/deltaforceguide/repository/FirearmRepository.java b/src/main/java/com/onixbyte/deltaforceguide/repository/FirearmRepository.java
index b486703..46c84b9 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/repository/FirearmRepository.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/repository/FirearmRepository.java
@@ -9,6 +9,11 @@ import org.springframework.stereotype.Repository;
 
 import java.util.List;
 
+/**
+ * Spring Data JPA repository for {@link Firearm} entity operations.
+ *
+ * @author zihluwang
+ */
 @Repository
 public interface FirearmRepository extends JpaRepository<Firearm, Long> {
 
diff --git a/src/main/java/com/onixbyte/deltaforceguide/repository/ModificationRepository.java b/src/main/java/com/onixbyte/deltaforceguide/repository/ModificationRepository.java
index d4f891a..3d9fcc0 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/repository/ModificationRepository.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/repository/ModificationRepository.java
@@ -13,6 +13,12 @@ import org.springframework.stereotype.Repository;
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Spring Data JPA repository for {@link Modification} entity operations,
+ * including native JSONB tag filtering for Postgres.
+ *
+ * @author zihluwang
+ */
 @Repository
 public interface ModificationRepository extends JpaRepository<Modification, Long> {
 
@@ -27,6 +33,14 @@ public interface ModificationRepository extends JpaRepository<Modification, Long
     @NonNull
     Optional<Modification> findById(@NonNull Long id);
 
+    /**
+     * Page query modifications with optional firearm and JSONB tag filtering.
+     *
+     * @param firearmId optional firearm ID filter (nullable)
+     * @param tagsJson  optional JSON array of tags to match via Postgres {@code @>} operator (nullable)
+     * @param pageable  pagination information
+     * @return a page of matching modifications
+     */
     @Query(value = """
             SELECT * FROM modification m
             WHERE (:firearmId IS NULL OR m.firearm_id = :firearmId)
@@ -40,6 +54,12 @@ public interface ModificationRepository extends JpaRepository<Modification, Long
             nativeQuery = true)
     Page<Modification> pageQueryByFirearmAndTags(@Param("firearmId") Long firearmId, @Param("tagsJson") String tagsJson, Pageable pageable);
 
+    /**
+     * Retrieve all distinct tag values from modifications, optionally filtered by firearm.
+     *
+     * @param firearmId optional firearm ID filter (nullable)
+     * @return list of distinct tag strings
+     */
     @Query(value = "SELECT DISTINCT jsonb_array_elements_text(cast(tags as jsonb)) FROM modification WHERE (:firearmId IS NULL OR firearm_id = :firearmId)", nativeQuery = true)
     List<String> findAllTags(@Param("firearmId") Long firearmId);
 }
diff --git a/src/main/java/com/onixbyte/deltaforceguide/repository/UserCredentialRepository.java b/src/main/java/com/onixbyte/deltaforceguide/repository/UserCredentialRepository.java
index 94fb8ec..53776e3 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/repository/UserCredentialRepository.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/repository/UserCredentialRepository.java
@@ -12,9 +12,20 @@ import org.springframework.stereotype.Repository;
 import java.util.List;
 import java.util.Optional;
 
+/**
+ * Spring Data JPA repository for {@link UserCredential} entity operations.
+ *
+ * @author zihluwang
+ */
 @Repository
 public interface UserCredentialRepository extends JpaRepository<UserCredential, UserCredentialId> {
 
+    /**
+     * Find all credentials belonging to a given user.
+     *
+     * @param userId the user ID
+     * @return list of matching credentials
+     */
     @EntityGraph(attributePaths = {"user"})
     @Query("""
             select uc
@@ -23,6 +34,13 @@ public interface UserCredentialRepository extends JpaRepository<UserCredential,
             """)
     List<UserCredential> findAllByUserId(@Param("userId") Long userId);
 
+    /**
+     * Find a specific credential for a user by provider.
+     *
+     * @param userId   the user ID
+     * @param provider the authentication provider identifier
+     * @return an optional containing the matching credential, or empty if not found
+     */
     @EntityGraph(attributePaths = {"user"})
     @Query("""
             select uc
@@ -32,6 +50,12 @@ public interface UserCredentialRepository extends JpaRepository<UserCredential,
             """)
     Optional<UserCredential> findByUserIdAndProvider(@Param("userId") Long userId, @Param("provider") String provider);
 
+    /**
+     * Delete a specific credential for a user by provider.
+     *
+     * @param userId   the user ID
+     * @param provider the authentication provider identifier
+     */
     @Modifying
     @Query("""
             delete from UserCredential uc
@@ -40,6 +64,11 @@ public interface UserCredentialRepository extends JpaRepository<UserCredential,
             """)
     void deleteByUserIdAndProvider(@Param("userId") Long userId, @Param("provider") String provider);
 
+    /**
+     * Delete all credentials for a given user.
+     *
+     * @param userId the user ID
+     */
     @Modifying
     @Query("""
             delete from UserCredential uc
diff --git a/src/main/java/com/onixbyte/deltaforceguide/repository/UserRepository.java b/src/main/java/com/onixbyte/deltaforceguide/repository/UserRepository.java
index 7cecaad..7a0a363 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/repository/UserRepository.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/repository/UserRepository.java
@@ -10,6 +10,11 @@ import org.springframework.stereotype.Repository;
 
 import java.util.Optional;
 
+/**
+ * Spring Data JPA repository for {@link User} entity operations.
+ *
+ * @author zihluwang
+ */
 @Repository
 public interface UserRepository extends JpaRepository<User, Long> {
 
@@ -28,6 +33,12 @@ public interface UserRepository extends JpaRepository<User, Long> {
 
     boolean existsByEmail(String email);
 
+    /**
+     * Find a user by either username or email.
+     *
+     * @param principal the username or email to search for
+     * @return an optional containing the matching user, or empty if not found
+     */
     @EntityGraph(attributePaths = {"credentials"})
     @Query("""
             select u
diff --git a/src/main/java/com/onixbyte/deltaforceguide/security/annotation/RequiresAuth.java b/src/main/java/com/onixbyte/deltaforceguide/security/annotation/RequiresAuth.java
index f022be3..9b6b014 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/security/annotation/RequiresAuth.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/security/annotation/RequiresAuth.java
@@ -7,6 +7,11 @@ import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
 
+/**
+ * Annotation to mark controller endpoints that require authentication.
+ *
+ * @author zihluwang
+ */
 @Target({ElementType.METHOD, ElementType.TYPE})
 @Retention(RetentionPolicy.RUNTIME)
 @PreAuthorize("isAuthenticated()")
diff --git a/src/main/java/com/onixbyte/deltaforceguide/security/authentication/UsernamePasswordAuthentication.java b/src/main/java/com/onixbyte/deltaforceguide/security/authentication/UsernamePasswordAuthentication.java
index 692efaf..9bd2ae3 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/security/authentication/UsernamePasswordAuthentication.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/security/authentication/UsernamePasswordAuthentication.java
@@ -8,6 +8,11 @@ import org.springframework.security.core.GrantedAuthority;
 import java.util.Collection;
 import java.util.List;
 
+/**
+ * Custom authentication token for username/password-based login flows.
+ *
+ * @author zihluwang
+ */
 public class UsernamePasswordAuthentication implements Authentication, CredentialsContainer {
     private final String username;
     private String password;
diff --git a/src/main/java/com/onixbyte/deltaforceguide/security/provider/UsernamePasswordAuthenticationProvider.java b/src/main/java/com/onixbyte/deltaforceguide/security/provider/UsernamePasswordAuthenticationProvider.java
index d5e9a65..01e6baa 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/security/provider/UsernamePasswordAuthenticationProvider.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/security/provider/UsernamePasswordAuthenticationProvider.java
@@ -17,6 +17,11 @@ import org.springframework.security.core.AuthenticationException;
 import org.springframework.security.crypto.password.PasswordEncoder;
 import org.springframework.stereotype.Component;
 
+/**
+ * Authentication provider that validates username/password credentials against stored BCrypt hashes.
+ *
+ * @author zihluwang
+ */
 @Component
 public class UsernamePasswordAuthenticationProvider implements AuthenticationProvider {
 
@@ -36,6 +41,12 @@ public class UsernamePasswordAuthenticationProvider implements AuthenticationPro
         this.userCredentialRepository = userCredentialRepository;
     }
 
+    /**
+     * Validates the username/password credentials against stored BCrypt hashes.
+     *
+     * @param authentication the authentication request object
+     * @return a fully authenticated object including user details
+     */
     @Override
     public Authentication authenticate(Authentication authentication) throws AuthenticationException {
         if (!(authentication instanceof UsernamePasswordAuthentication usernamePasswordAuthentication)) {
@@ -75,6 +86,12 @@ public class UsernamePasswordAuthenticationProvider implements AuthenticationPro
         return usernamePasswordAuthentication;
     }
 
+    /**
+     * Checks if this provider supports the given authentication type.
+     *
+     * @param authentication the authentication class to check
+     * @return true if this provider supports the given type
+     */
     @Override
     public boolean supports(Class<?> authentication) {
         return UsernamePasswordAuthentication.class.isAssignableFrom(authentication);
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/AuthService.java b/src/main/java/com/onixbyte/deltaforceguide/service/AuthService.java
index b1bbfc7..da41902 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/AuthService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/AuthService.java
@@ -10,9 +10,11 @@ import org.springframework.http.HttpStatus;
 import org.springframework.security.authentication.AuthenticationManager;
 import org.springframework.stereotype.Service;
 
-import java.util.Objects;
-import java.util.Optional;
-
+/**
+ * Service handling user authentication, login, and session management.
+ *
+ * @author zihluwang
+ */
 @Service
 public class AuthService {
 
@@ -23,6 +25,16 @@ public class AuthService {
         this.authenticationManager = authenticationManager;
     }
 
+    /**
+     * Authenticates a user with the given login credentials.
+     * <p>
+     * Delegates authentication to Spring Security's {@link AuthenticationManager} and verifies
+     * that the result is of the expected {@link UsernamePasswordAuthentication} type.
+     *
+     * @param request the login credentials containing principle and password
+     * @return the authenticated {@link User}
+     * @throws BizException if authentication fails or the result type is unexpected
+     */
     public User login(LoginRequest request) {
         var _authentication = authenticationManager.authenticate(UsernamePasswordAuthentication
                 .unauthenticated(request.principle(), request.credential()));
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/CookieService.java b/src/main/java/com/onixbyte/deltaforceguide/service/CookieService.java
index 764b47b..eb93086 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/CookieService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/CookieService.java
@@ -6,6 +6,11 @@ import org.springframework.stereotype.Service;
 
 import java.time.Duration;
 
+/**
+ * Service for building HTTP cookies with configurable properties.
+ *
+ * @author zihluwang
+ */
 @Service
 public class CookieService {
 
@@ -15,10 +20,25 @@ public class CookieService {
         this.cookieManager = cookieManager;
     }
 
+    /**
+     * Builds a response cookie with the default max age from configuration.
+     *
+     * @param cookieName the cookie name
+     * @param value      the cookie value
+     * @return a configured ResponseCookie
+     */
     public ResponseCookie buildCookie(String cookieName, String value) {
         return buildCookieInternal(cookieName, value, cookieManager.getMaxAge());
     }
 
+    /**
+     * Builds a response cookie with a custom valid duration.
+     *
+     * @param cookieName    the cookie name
+     * @param value         the cookie value
+     * @param validDuration the cookie's max age
+     * @return a configured ResponseCookie
+     */
     public ResponseCookie buildCookie(String cookieName, String value, Duration validDuration) {
         return buildCookieInternal(cookieName, value, validDuration);
     }
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/DailyPasswordService.java b/src/main/java/com/onixbyte/deltaforceguide/service/DailyPasswordService.java
index 3ad3d4e..fa2118d 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/DailyPasswordService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/DailyPasswordService.java
@@ -4,6 +4,11 @@ import com.onixbyte.deltaforceguide.domain.dto.DailyPasswordResponse;
 import com.onixbyte.deltaforceguide.manager.DailyPasswordManager;
 import org.springframework.stereotype.Service;
 
+/**
+ * Service for generating and caching daily rotation passwords.
+ *
+ * @author zihluwang
+ */
 @Service
 public class DailyPasswordService {
 
@@ -13,6 +18,10 @@ public class DailyPasswordService {
         this.dailyPasswordManager = dailyPasswordManager;
     }
 
+    /**
+     * Retrieves the daily password for the current day.
+     * @return the daily password response
+     */
     public DailyPasswordResponse getDailyPassword() {
         return dailyPasswordManager.getDailyPassword();
     }
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/FirearmService.java b/src/main/java/com/onixbyte/deltaforceguide/service/FirearmService.java
index 3b69c15..5f5098b 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/FirearmService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/FirearmService.java
@@ -11,9 +11,13 @@ import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
-import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.server.ResponseStatusException;
 
+/**
+ * Service handling firearm business logic including CRUD operations and queries.
+ *
+ * @author zihluwang
+ */
 @Service
 public class FirearmService {
 
@@ -23,7 +27,13 @@ public class FirearmService {
         this.firearmRepository = firearmRepository;
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Queries firearms with optional type filter and pagination.
+     *
+     * @param type optional firearm type filter
+     * @param pageable pagination parameters
+     * @return a paginated response of firearm records
+     */
     public PageResponse<FirearmResponse> pageQuery(FirearmType type, Pageable pageable) {
         Page<Firearm> page = type == null
                 ? firearmRepository.findAll(pageable)
@@ -32,13 +42,24 @@ public class FirearmService {
         return PageResponse.from(page.map(FirearmResponse::from));
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a firearm by its ID.
+     *
+     * @param id the firearm ID
+     * @return the firearm response
+     */
     public FirearmResponse queryById(Long id) {
         return firearmRepository.findById(id)
                 .map(FirearmResponse::from)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Firearm not found: " + id));
     }
 
+    /**
+     * Creates a new firearm from the provided request data.
+     *
+     * @param request the firearm creation request
+     * @return the created firearm response
+     */
     public FirearmResponse addFirearm(FirearmRequest request) {
         var firearm = firearmRepository.save(Firearm.builder()
                 .name(request.name())
@@ -54,7 +75,13 @@ public class FirearmService {
         return FirearmResponse.from(firearm);
     }
 
-    @Transactional
+    /**
+     * Updates an existing firearm identified by ID.
+     *
+     * @param id the firearm ID
+     * @param request the updated firearm data
+     * @return the updated firearm response
+     */
     public FirearmResponse updateFirearm(Long id, FirearmRequest request) {
         var firearm = firearmRepository.findById(id)
                 .orElseThrow(() -> new BizException(HttpStatus.NOT_FOUND, "Firearm not found: " + id));
@@ -71,7 +98,11 @@ public class FirearmService {
         return FirearmResponse.from(firearmRepository.save(firearm));
     }
 
-    @Transactional
+    /**
+     * Deletes a firearm by its ID.
+     *
+     * @param id the firearm ID to delete
+     */
     public void deleteFirearm(Long id) {
         Firearm firearm = firearmRepository.findById(id)
                 .orElseThrow(() -> new BizException(HttpStatus.NOT_FOUND, "Firearm not found: " + id));
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/ModificationService.java b/src/main/java/com/onixbyte/deltaforceguide/service/ModificationService.java
index 37aa1d4..9b97e8f 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/ModificationService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/ModificationService.java
@@ -18,7 +18,6 @@ import org.springframework.data.domain.Page;
 import org.springframework.data.domain.Pageable;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
-import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.server.ResponseStatusException;
 
 import java.util.ArrayList;
@@ -26,6 +25,11 @@ import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 
+/**
+ * Service handling modification business logic including CRUD, batch operations, and tag filtering.
+ *
+ * @author zihluwang
+ */
 @Service
 public class ModificationService {
 
@@ -46,7 +50,14 @@ public class ModificationService {
         this.objectMapper = objectMapper;
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Queries modifications with optional firearm and tag filters.
+     *
+     * @param firearmId optional firearm ID filter
+     * @param tags optional tag list filter
+     * @param pageable pagination parameters
+     * @return a paginated response of modification records
+     */
     public PageResponse<ModificationResponse> pageQuery(Long firearmId, List<String> tags, Pageable pageable) {
         String tagsJson = null;
         if (tags != null && !tags.isEmpty()) {
@@ -67,27 +78,55 @@ public class ModificationService {
         return PageResponse.from(page.map(ModificationResponse::from));
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a modification by its ID.
+     *
+     * @param id the modification ID
+     * @return the modification response
+     */
     public ModificationResponse queryById(Long id) {
         return modificationRepository.findById(id)
                 .map(ModificationResponse::from)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Modification not found: " + id));
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds all unique tags across modifications, optionally scoped to a firearm.
+     *
+     * @param firearmId optional firearm ID to scope the tag search
+     * @return list of unique tag strings
+     */
     public List<String> findAllTags(Long firearmId) {
         return modificationRepository.findAllTags(firearmId);
     }
 
+    /**
+     * Creates a new modification for a given firearm.
+     *
+     * @param request the modification creation request
+     * @return the created modification response
+     */
     public ModificationResponse create(ModificationRequest request) {
         return modificationManager.create(request);
     }
 
+    /**
+     * Creates multiple modifications in a single batch operation.
+     *
+     * @param requests list of modification creation requests
+     * @return list of created modification responses
+     */
     public List<ModificationResponse> batchCreate(List<ModificationRequest> requests) {
         return modificationManager.batchCreate(requests);
     }
 
-    @Transactional
+    /**
+     * Updates an existing modification identified by ID.
+     *
+     * @param id the modification ID
+     * @param request the updated modification data
+     * @return the updated modification response
+     */
     public ModificationResponse update(Long id, ModificationRequest request) {
         Modification modification = modificationRepository.findById(id)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Modification not found: " + id));
@@ -106,14 +145,22 @@ public class ModificationService {
         return ModificationResponse.from(modificationRepository.save(modification));
     }
 
-    @Transactional
+    /**
+     * Deletes a modification by its ID.
+     *
+     * @param id the modification ID to delete
+     */
     public void delete(Long id) {
         Modification modification = modificationRepository.findById(id)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "Modification not found: " + id));
         modificationRepository.delete(modification);
     }
 
-    @Transactional
+    /**
+     * Deletes multiple modifications in a single batch operation.
+     *
+     * @param ids list of modification IDs to delete
+     */
     public void batchDelete(List<Long> ids) {
         Set<Long> uniqueIds = new LinkedHashSet<>(ids);
         List<Modification> modifications = modificationRepository.findAllById(uniqueIds);
diff --git a/src/main/java/com/onixbyte/deltaforceguide/service/UserService.java b/src/main/java/com/onixbyte/deltaforceguide/service/UserService.java
index c57ce4f..700e26d 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/service/UserService.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/service/UserService.java
@@ -6,11 +6,15 @@ import com.onixbyte.deltaforceguide.manager.UserCredentialManager;
 import com.onixbyte.deltaforceguide.manager.UserManager;
 import org.springframework.http.HttpStatus;
 import org.springframework.stereotype.Service;
-import org.springframework.transaction.annotation.Transactional;
 import org.springframework.web.server.ResponseStatusException;
 
 import java.util.List;
 
+/**
+ * Service for user account management and profile operations.
+ *
+ * @author zihluwang
+ */
 @Service
 public class UserService {
 
@@ -22,29 +26,53 @@ public class UserService {
         this.userCredentialManager = userCredentialManager;
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Retrieves all registered users.
+     *
+     * @return list of all users
+     */
     public List<User> findAll() {
         return userManager.findAll();
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a user by their ID.
+     *
+     * @param id the user ID
+     * @return the user
+     */
     public User queryById(Long id) {
         return userManager.findById(id)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found: " + id));
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds a user by their username.
+     *
+     * @param username the username to search for
+     * @return the user
+     */
     public User queryByUsername(String username) {
         return userManager.findByUsername(username)
                 .orElseThrow(() -> new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found: " + username));
     }
 
-    @Transactional
+    /**
+     * Creates a new user account.
+     *
+     * @param user the user entity to persist
+     * @return the saved user entity
+     */
     public User create(User user) {
         return userManager.save(user);
     }
 
-    @Transactional
+    /**
+     * Updates an existing user account.
+     *
+     * @param user the user entity with updated fields
+     * @return the saved user entity
+     */
     public User update(User user) {
         if (user.getId() == null || userManager.findById(user.getId()).isEmpty()) {
             throw new ResponseStatusException(HttpStatus.NOT_FOUND, "User not found: " + user.getId());
@@ -52,13 +80,24 @@ public class UserService {
         return userManager.save(user);
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Finds all credentials associated with a user.
+     *
+     * @param userId the user ID
+     * @return list of user credentials
+     */
     public List<UserCredential> findCredentials(Long userId) {
         ensureUserExists(userId);
         return userCredentialManager.findAllByUserId(userId);
     }
 
-    @Transactional(readOnly = true)
+    /**
+     * Queries a specific credential for a user by provider.
+     *
+     * @param userId   the user ID
+     * @param provider the authentication provider
+     * @return the matching credential
+     */
     public UserCredential queryCredential(Long userId, String provider) {
         ensureUserExists(userId);
         return userCredentialManager.findByUserIdAndProvider(userId, provider)
@@ -67,7 +106,14 @@ public class UserService {
                         "User credential not found: userId=" + userId + ", provider=" + provider));
     }
 
-    @Transactional
+    /**
+     * Creates or updates a credential for a user and provider.
+     *
+     * @param userId     the user ID
+     * @param provider   the authentication provider
+     * @param credential the credential value
+     * @return the saved credential
+     */
     public UserCredential upsertCredential(Long userId, String provider, String credential) {
         User user = ensureUserExists(userId);
         UserCredential userCredential = userCredentialManager.findByUserIdAndProvider(userId, provider)
@@ -78,13 +124,22 @@ public class UserService {
         return userCredentialManager.save(userCredential);
     }
 
-    @Transactional
+    /**
+     * Deletes a specific credential for a user by provider.
+     *
+     * @param userId   the user ID
+     * @param provider the authentication provider
+     */
     public void deleteCredential(Long userId, String provider) {
         ensureUserExists(userId);
         userCredentialManager.deleteByUserIdAndProvider(userId, provider);
     }
 
-    @Transactional
+    /**
+     * Deletes a user and all associated credentials.
+     *
+     * @param id the user ID to delete
+     */
     public void deleteById(Long id) {
         ensureUserExists(id);
         userCredentialManager.deleteAllByUserId(id);
diff --git a/src/main/java/com/onixbyte/deltaforceguide/shared/CookieName.java b/src/main/java/com/onixbyte/deltaforceguide/shared/CookieName.java
index 329852b..26f0112 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/shared/CookieName.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/shared/CookieName.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.shared;
 
+/**
+ * Constants for HTTP cookie names used for authentication tokens.
+ *
+ * @author zihluwang
+ */
 public class CookieName {
 
     public static final String ACCESS_TOKEN = "AccessToken";
diff --git a/src/main/java/com/onixbyte/deltaforceguide/shared/CredentialProvider.java b/src/main/java/com/onixbyte/deltaforceguide/shared/CredentialProvider.java
index 115f935..9488536 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/shared/CredentialProvider.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/shared/CredentialProvider.java
@@ -1,5 +1,10 @@
 package com.onixbyte.deltaforceguide.shared;
 
+/**
+ * Constants for supported authentication provider identifiers.
+ *
+ * @author zihluwang
+ */
 public class CredentialProvider {
 
     public static final String LOCAL = "LOCAL";
diff --git a/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonModules.java b/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonModules.java
index 36332aa..ae47823 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonModules.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonModules.java
@@ -13,6 +13,12 @@ import java.time.LocalDate;
 import java.time.LocalDateTime;
 import java.time.LocalTime;
 
+/**
+ * Shared Jackson {@link com.fasterxml.jackson.databind.Module} instances for custom date/time
+ * serialisation and deserialisation across the application.
+ *
+ * @author zihluwang
+ */
 public class JacksonModules {
 
     public static final SimpleModule DATE_TIME_MODULE = initialiseDateTimeModule();
diff --git a/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonRedisSerialiser.java b/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonRedisSerialiser.java
index 5a300ba..4e50c38 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonRedisSerialiser.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/shared/JacksonRedisSerialiser.java
@@ -4,6 +4,12 @@ import com.fasterxml.jackson.databind.SerializationFeature;
 import com.fasterxml.jackson.datatype.jsr310.JavaTimeModule;
 import org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer;
 
+/**
+ * Singleton serialiser for Redis cache operations using
+ * {@link GenericJackson2JsonRedisSerializer} with JavaTime module support.
+ *
+ * @author zihluwang
+ */
 public class JacksonRedisSerialiser {
 
     public static final GenericJackson2JsonRedisSerializer INSTANCE = initialiseSerializer();
diff --git a/src/main/java/com/onixbyte/deltaforceguide/utils/DateTimeUtil.java b/src/main/java/com/onixbyte/deltaforceguide/utils/DateTimeUtil.java
index f1360c8..1d576a5 100644
--- a/src/main/java/com/onixbyte/deltaforceguide/utils/DateTimeUtil.java
+++ b/src/main/java/com/onixbyte/deltaforceguide/utils/DateTimeUtil.java
@@ -4,8 +4,19 @@ import java.time.Instant;
 import java.time.LocalDateTime;
 import java.time.ZoneId;
 
+/**
+ * Utility class for date and time operations using system-default time zone.
+ *
+ * @author zihluwang
+ */
 public class DateTimeUtil {
 
+    /**
+     * Convert a {@link LocalDateTime} to an {@link Instant} using the system-default time zone.
+     *
+     * @param ldt the local date-time to convert
+     * @return the corresponding instant
+     */
     public static Instant asInstant(LocalDateTime ldt) {
         return ldt.atZone(ZoneId.systemDefault())
                 .toInstant();