diff --git a/CLAUDE.md b/CLAUDE.md
new file mode 100644
index 00000000..0f0cb9af
--- /dev/null
+++ b/CLAUDE.md
@@ -0,0 +1,207 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+CCS (Claude Code Switch) is a lightweight CLI wrapper enabling instant profile switching between Claude Sonnet 4.5 and GLM 4.6 models. The tool delegates to the official Claude CLI via the `--settings` flag, supporting both Unix-like systems (bash) and Windows (PowerShell).
+
+**Primary Installation Methods** (highest priority):
+- macOS/Linux: `curl -fsSL ccs.kaitran.ca/install | bash`
+- Windows: `irm ccs.kaitran.ca/install | iex`
+
+## Core Design Principles
+
+**YAGNI** (You Aren't Gonna Need It): No features "just in case"
+**KISS** (Keep It Simple): Simple bash/PowerShell, no complexity
+**DRY** (Don't Repeat Yourself): One source of truth (config.json)
+
+The tool does ONE thing: map profile names to Claude settings files. Never add features that violate these principles.
+
+## Key Constraints
+
+1. **NO EMOJIS in terminal output** - Users of this `ccs` project may lack encoders by default. Try to find alternatives to illustrate signals
+2. **Idempotent installations** - Running install scripts multiple times must be safe
+3. **Non-invasive** - Never modify `~/.claude/settings.json`
+4. **Cross-platform parity** - Identical behavior on Unix/Linux/macOS/Windows
+5. **Edge case handling** - Handle all scenarios gracefully (see tests/edge-cases.sh)
+
+## Architecture
+
+```
+User: ccs [profile] [claude-args]
+  ↓
+Read ~/.ccs/config.json
+  ↓
+Lookup profile → settings file path
+  ↓
+Validate settings file exists
+  ↓
+exec claude --settings <path> [args]
+```
+
+**Key Files**:
+- `ccs` (bash) / `ccs.ps1` (PowerShell): Main executable wrapper
+- `installers/install.sh` / `installers/install.ps1`: Installation scripts
+- `installers/uninstall.sh` / `installers/uninstall.ps1`: Removal scripts
+- `VERSION`: Single source of truth for version (format: MAJOR.MINOR.PATCH)
+- `.claude/`: Commands and skills for Claude Code integration
+
+**Installation Creates**:
+```
+~/.ccs/
+├── ccs                     # Main executable (or ccs.ps1 on Windows)
+├── config.json             # Profile mappings
+├── config.json.backup      # Single backup (overwrites on each install)
+├── glm.settings.json       # GLM profile template
+├── VERSION                 # Version file copy
+├── uninstall.sh            # Uninstaller (or ccs-uninstall.ps1 on Windows)
+└── .claude/                # Claude Code integration
+    ├── commands/ccs.md
+    └── skills/ccs-delegation/
+```
+
+## Development Commands
+
+### Version Management
+```bash
+# Bump version (updates VERSION, install.sh, install.ps1)
+./scripts/bump-version.sh [major|minor|patch]
+
+# Get current version
+cat VERSION
+# or
+./scripts/get-version.sh
+```
+
+### Testing
+```bash
+# Comprehensive edge case testing (Unix)
+./tests/edge-cases.sh
+
+# Comprehensive edge case testing (Windows)
+./tests/edge-cases.ps1
+```
+
+### Local Development
+```bash
+# Test local installation from git repo
+./installers/install.sh
+
+# Test with local executable
+./ccs --version
+./ccs glm --help
+
+# Clean test environment
+rm -rf ~/.ccs
+```
+
+## Code Standards
+
+### Bash (Unix Systems)
+- Compatibility: bash 3.2+ (macOS default)
+- Always quote variables: `"$VAR"` not `$VAR`
+- Use `[[ ]]` for tests, not `[ ]`
+- Use `#!/usr/bin/env bash` shebang
+- Set `set -euo pipefail` for safety
+- Dependencies: Only `jq` for JSON parsing
+
+### PowerShell (Windows)
+- Compatibility: PowerShell 5.1+
+- Use `$ErrorActionPreference = "Stop"`
+- Native JSON parsing via `ConvertFrom-Json` / `ConvertTo-Json`
+- No external dependencies required
+
+### Version Synchronization
+When changing version, update ALL three locations:
+1. `VERSION` file
+2. `installers/install.sh` (CCS_VERSION variable)
+3. `installers/install.ps1` ($CcsVersion variable)
+
+Use `./scripts/bump-version.sh` to update all locations atomically.
+
+## Critical Implementation Details
+
+### Profile Detection Logic
+The `ccs` wrapper uses smart detection:
+- No args OR first arg starts with `-` → use default profile
+- First arg doesn't start with `-` → treat as profile name
+- Special flags handled BEFORE profile detection: `--version`, `-v`, `--help`, `-h`, `--install`
+
+### Installation Modes
+- **Git mode**: Running from cloned repository (symlinks executables)
+- **Standalone mode**: Running via curl/irm (downloads from GitHub)
+
+Detection: Check if `ccs` executable exists in script directory or parent.
+
+### Idempotency Requirements
+Install scripts must be safe to run multiple times:
+- Check existing files before creating
+- Use single backup file (no timestamps): `config.json.backup`
+- Skip existing `.claude/` folder installation
+- Handle both clean and existing installations
+
+### Settings File Format
+```json
+{
+  "env": {
+    "ANTHROPIC_BASE_URL": "https://api.z.ai/api/anthropic",
+    "ANTHROPIC_AUTH_TOKEN": "your_api_key",
+    "ANTHROPIC_MODEL": "glm-4.6",
+    "ANTHROPIC_DEFAULT_OPUS_MODEL": "glm-4.6",
+    "ANTHROPIC_DEFAULT_SONNET_MODEL": "glm-4.6",
+    "ANTHROPIC_DEFAULT_HAIKU_MODEL": "glm-4.6"
+  }
+}
+```
+
+All values must be strings (not booleans/objects) to prevent PowerShell crashes.
+
+## Common Tasks
+
+### Adding a New Feature
+1. Verify it aligns with YAGNI/KISS/DRY principles
+2. Implement for both bash and PowerShell
+3. Test on all platforms (macOS, Linux, Windows)
+4. Update tests in `tests/edge-cases.sh` and `tests/edge-cases.ps1`
+5. Update relevant documentation in `docs/`
+
+### Fixing Bugs
+1. Add test case reproducing the bug
+2. Fix in both bash and PowerShell versions
+3. Verify fix doesn't break existing tests
+4. Test on all supported platforms
+
+### Releasing New Version
+1. Run `./scripts/bump-version.sh [major|minor|patch]`
+2. Review changes to VERSION, install.sh, install.ps1
+3. Test installation from both git and standalone modes
+4. Run full edge case test suite
+5. Commit and tag: `git tag v<VERSION>`
+
+## Testing Requirements
+
+Before any PR, verify:
+- [ ] Works on macOS (bash)
+- [ ] Works on Linux (bash)
+- [ ] Works on Windows (PowerShell)
+- [ ] Works on Windows (Git Bash)
+- [ ] Handles all edge cases in test suite
+- [ ] Installation is idempotent
+- [ ] No emojis in terminal output
+- [ ] Version displayed correctly
+
+## Integration with Claude Code
+
+The `.claude/` folder contains:
+- `/ccs` command: Meta-command for delegating tasks to different models
+- `ccs-delegation` skill: Intelligent task delegation patterns
+
+Install with: `ccs --install` (copies to `~/.claude/`)
+
+## Error Handling Philosophy
+
+- Validate early, fail fast with clear error messages
+- Show available options when user makes mistake
+- Suggest recovery steps (e.g., restore from backup)
+- Never leave system in broken state