diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..5767357
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,109 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Coding Standards
+
+- **Style**: Follow the Google Java Coding Style as the foundation.
+- **Indentation**: Use 4 spaces — no tabs.
+- **Line length**: Maximum 100 characters per line.
+- **Comments**: All code comments must use British English spelling (e.g. "colour" not "color", "behaviour" not "behavior", "serialise" not "serialize", "analyse" not "analyze", "traveller" not "traveler").
+
+## Build & Test Commands
+
+```bash
+# Build the project (skip tests)
+./gradlew build -x test
+
+# Run all tests
+./gradlew test
+
+# Run a single test class
+./gradlew test --tests "com.onixbyte.deltaforceguide.service.PasswordEncoderTest"
+
+# Run a specific test method
+./gradlew test --tests "com.onixbyte.deltaforceguide.service.PasswordEncoderTest.generatePassword"
+
+# Build the full JAR
+./gradlew bootJar
+```
+
+The project uses Gradle with Java 21 (Amazon Corretto). Tests use JUnit 5 with the Spring Boot test framework, H2 in-memory database for test runtime, and Spring Security test support. Tests require an active `dev` profile.
+
+## Code Architecture
+
+**Delta Force Guide Server** — A REST API backend for managing Delta Force game firearm builds/modifications.
+
+### Package structure
+
+```
+com.onixbyte.deltaforceguide
+├── client/           # External service clients (TokenClient for JWT)
+├── config/           # Spring beans: Security, CORS, Cache/Redis, Jackson, MyBatis, Spring Data
+├── controller/       # REST controllers (Firearm, Modification, Tag, Auth)
+├── domain/
+│   ├── converter/    # JPA attribute converters (FirearmTypeConverter)
+│   ├── dto/          # Request/response records (FirearmRequest, ModificationResponse, etc.)
+│   └── entity/       # JPA entities (Firearm, Modification, User, Accessory, Tuning)
+├── enumeration/      # Enums (FirearmType)
+├── exeption/         # BizException (custom runtime exception with HTTP status)
+├── filter/           # TokenAuthenticationFilter (JWT auth via OncePerRequestFilter)
+├── manager/          # Thin @Transactional wrappers around repositories
+├── mapper/           # MyBatis mappers (configured but currently unused)
+├── properties/       # @ConfigurationProperties records (Cors, Token, Cookie)
+├── repository/       # Spring Data JPA repositories
+├── security/
+│   ├── authentication/  # Custom UsernamePasswordAuthentication impl
+│   └── provider/        # UsernamePasswordAuthenticationProvider
+├── service/          # Business logic layer (FirearmService, ModificationService, AuthService, etc.)
+├── shared/           # Constants and utility classes (CookieName, CredentialProvider, JacksonModules)
+└── utils/            # Helpers (DateTimeUtil)
+```
+
+### Key design decisions
+
+- **JPA + native queries**: Most CRUD uses Spring Data JPA. Native queries (in `ModificationRepository`) handle JSONB tag filtering with Postgres `@>` operator.
+- **Custom auth flow**: JWT tokens in httpOnly cookies (`AccessToken`). Spring Security with a custom `UsernamePasswordAuthenticationProvider` and `TokenAuthenticationFilter`. Tokens are auto-renewed within 5 min of expiry.
+- **JSONB storage**: `Modification.tags` and `Modification.accessories` (including nested `Tuning` objects) are stored as JSONB columns using Hypersistence Utils `JsonType`.
+- **Manager layer**: `UserManager` and `UserCredentialManager` sit between service and repository, adding `@Transactional` boundaries without mixing concerns.
+- **DTOs as Java records**: All request/response objects are immutable records with static `from()` factory methods for entity→DTO conversion.
+- **Flyway migrations**: SQL migrations in `src/main/resources/db/migration/` — V2 (init), V3 (bullet/damage fields), V4 (user), V5 (accessories JSONB column).
+
+### Data model
+
+- `firearm` table: id, name, type (int→FirearmType enum), level, calibre, fire_rate, armour_damage, body_damage, review
+- `modification` table: id, firearm_id (FK→firearm), name, code, tags (jsonb), accessories (jsonb), note, author, video_url
+- `app_user` table: id, username, email
+- `user_credential` table: user_id, provider, credential (hashed)
+
+### API endpoints
+
+| Path | Methods | Auth |
+|---|---|---|
+| `/firearms` | GET, POST | GET public, POST requires auth |
+| `/firearms/{id}` | GET, PUT, DELETE | GET public, PUT/DELETE requires auth |
+| `/modifications` | GET, POST | GET public, POST requires auth |
+| `/modifications/{id}` | GET, PUT, DELETE | GET public, PUT/DELETE requires auth |
+| `/modifications/batch` | POST | Requires auth |
+| `/modifications/batch-delete` | DELETE | Requires auth |
+| `/tags` | GET | Public |
+| `/auth/login` | POST | Public |
+| `/auth/logout` | POST | Authenticated |
+
+### Commit convention
+
+Conventional commits: `feat:`, `chore:`, `fix:`. Messages are in English, present tense imperative style.
+
+### External dependencies
+
+- **DB**: PostgreSQL (via Flyway migrations), H2 in test
+- **Cache**: Redis (via Spring Cache + RedisTemplate with GenericJackson2JsonRedisSerializer)
+- **Auth**: java-jwt (auth0), BCrypt
+- **Docs**: springdoc-openapi (Swagger UI) on dev profile
+- **Onixbyte internal libs**: version-catalogue, tuple, common-toolbox, math-toolbox, identity-generator, captcha, regions
+- **AWS**: S3 SDK
+
+### Profiles
+
+- `dev`: Enables Swagger UI, connects to dev DB/Redis at `dfguide.onixbyte.cn`. Config in `config/application-dev.yaml`.
+- Default profile: Used for production, no Swagger, connects to production datasource.
diff --git a/build.gradle b/build.gradle
new file mode 100644
index 0000000..b1aeb5f
--- /dev/null
+++ b/build.gradle
@@ -0,0 +1,37 @@
+plugins {
+    id 'java'
+    id 'org.springframework.boot' version '3.5.13'
+    id 'io.spring.dependency-management' version '1.1.7'
+}
+
+group = 'com.onixbyte'
+version = '0.0.1-SNAPSHOT'
+description = 'delta-force-guide-server'
+
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter-cache'
+    implementation 'org.springframework.boot:spring-boot-starter-data-jpa'
+    implementation 'org.springframework.boot:spring-boot-starter-data-redis'
+    implementation 'org.springframework.boot:spring-boot-starter-security'
+    implementation 'org.springframework.boot:spring-boot-starter-validation'
+    implementation 'org.springframework.boot:spring-boot-starter-web'
+    implementation 'org.springdoc:springdoc-openapi-starter-webmvc-ui:2.8.16'
+    runtimeOnly 'org.postgresql:postgresql'
+    testImplementation 'org.springframework.boot:spring-boot-starter-test'
+    testImplementation 'org.springframework.security:spring-security-test'
+    testRuntimeOnly 'org.junit.platform:junit-platform-launcher'
+}
+
+tasks.named('test') {
+    useJUnitPlatform()
+}
diff --git a/settings.gradle b/settings.gradle
new file mode 100644
index 0000000..3da6727
--- /dev/null
+++ b/settings.gradle
@@ -0,0 +1 @@
+rootProject.name = 'delta-force-guide-server'
diff --git a/src/main/java/com/onixbyte/deltaforceguide/domain/entity/FirearmTypeConverter.java b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/FirearmTypeConverter.java
new file mode 100644
index 0000000..03f7574
--- /dev/null
+++ b/src/main/java/com/onixbyte/deltaforceguide/domain/entity/FirearmTypeConverter.java
@@ -0,0 +1,20 @@
+package com.onixbyte.deltaforceguide.domain.entity;
+
+import com.onixbyte.deltaforceguide.enumeration.FirearmType;
+import jakarta.persistence.AttributeConverter;
+import jakarta.persistence.Converter;
+
+@Converter(autoApply = false)
+public class FirearmTypeConverter implements AttributeConverter<FirearmType, Integer> {
+
+    @Override
+    public Integer convertToDatabaseColumn(FirearmType attribute) {
+        return attribute == null ? null : attribute.getCode();
+    }
+
+    @Override
+    public FirearmType convertToEntityAttribute(Integer dbData) {
+        return FirearmType.fromCode(dbData);
+    }
+}
+