diff --git a/.github/workflows/test-and-release.yml b/.github/workflows/test-and-release.yml
index ba04c12..e44f5d6 100644
--- a/.github/workflows/test-and-release.yml
+++ b/.github/workflows/test-and-release.yml
@@ -3,11 +3,10 @@ name: Test and Release
 on:
   pull_request:
   push:
-    branches: [ master ]
-    tags: ['*']
+    branches: [master]
+    tags: ["*"]
 
 jobs:
-
   test:
     runs-on: ubuntu-latest
     services:
@@ -63,6 +62,9 @@ jobs:
       - name: Composer install
         run: composer update --optimize-autoloader --prefer-dist
 
+      - name: Install subversion
+        run: sudo apt-get update && sudo apt-get install -y subversion
+
       - name: Install WP Tests
         run: bash bin/install-wp-tests.sh wordpress_test root root 127.0.0.1 ${{ matrix.wp }} true
 
@@ -76,7 +78,7 @@ jobs:
           WP_MULTISITE=1 composer test
 
   lint:
-    runs-on:  ubuntu-latest
+    runs-on: ubuntu-latest
     name: PHP lint
     steps:
       - uses: actions/checkout@v4
@@ -106,7 +108,7 @@ jobs:
   release:
     name: Release
     runs-on: ubuntu-latest
-    needs: [test,lint]
+    needs: [test, lint]
     steps:
       - uses: actions/checkout@v4
       - name: Build
diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 0000000..6cc1da1
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,76 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+**Custom Post Type Permalinks** is a WordPress plugin that allows editing the permalink structure of custom post types. It is listed in the official WordPress.org plugin directory.
+
+## Commands
+
+### Testing
+
+WordPress test environment setup is required before running tests:
+
+```bash
+bash bin/install-wp-tests.sh <db-name> <db-user> <db-pass> [db-host] [wp-version]
+# Example: bash bin/install-wp-tests.sh wordpress_test root root 127.0.0.1 trunk
+```
+
+```bash
+# Run tests
+composer test
+
+# Run tests in multisite mode
+WP_MULTISITE=1 composer test
+```
+
+### Lint / Code Quality
+
+```bash
+# PHPCS check (WordPress Coding Standards)
+composer phpcs
+
+# Auto-format
+composer format
+```
+
+## Architecture
+
+### Design Pattern
+
+The plugin uses a **singleton + modular architecture**:
+
+- `custom-post-type-permalinks.php` — Plugin entry point. Defines constants and class autoloader.
+- `CPTP.php` — Singleton main class. Initializes modules sequentially via `CPTP::get_instance()->init()`.
+- `CPTP/Module.php` — Abstract base class for all modules.
+- `CPTP/Util.php` — Utility functions for retrieving post types, checking rewrite support, etc.
+
+### Modules (`CPTP/Module/`)
+
+| Module | Responsibility |
+|--------|---------------|
+| `Setting` | Text domain loading, version management |
+| `Rewrite` | Registers rewrite rules for custom post types and taxonomies |
+| `Admin` | Settings UI (Settings → Permalinks) |
+| `Option` | Saves permalink structure options |
+| `Permalink` | Generates permalinks for posts, terms, and archives |
+| `GetArchives` | Supports `wp_get_archives()` |
+| `FlushRules` | Handles rewrite rule flushing |
+
+To add or modify modules, use the `CPTP_load_modules` / `cptp_load_modules` hooks.
+
+### Coding Standards
+
+- Prefix: `CPTP`
+- Text domain: `custom-post-type-permalinks`
+- WordPress Coding Standards (including Yoda conditions)
+- PHP 7.4+
+
+### Tests
+
+PHPUnit tests under `tests/`. `tests/bootstrap.php` initializes the WordPress test environment and Yoast PHPUnit Polyfills.
+
+### CI/CD
+
+`.github/workflows/test-and-release.yml` runs tests across PHP 7.4/8.0/8.2 and WP trunk/6.5/6.1. Automatically deploys to WordPress.org on tag creation.