Context Guard

---
name: context-guard
description: Installs opt-in Claude Code hooks that detect stale AI context files (CLAUDE.md, AGENTS.md, GEMINI.md, etc.) and remind developers to update them. Includes post-commit drift detection, structural change reminders, and a quality rule. Claude Code only — hooks do not work in OpenCode, Codex CLI, or other tools.
version: "1.0.0"
---

# Context Guard

## What It Does

Context Guard adds two PostToolUse hooks and one quality rule to a project. The hooks detect when AI context files (CLAUDE.md, AGENTS.md, GEMINI.md, .cursorrules, copilot-instructions.md, .windsurfrules, .clinerules) are out of date and nudge the developer to update them.

**Claude Code only.** These hooks use Claude Code's hook system (PostToolUse events, `.claude/settings.json` configuration). OpenCode, Codex CLI, Cursor, Windsurf, Cline, and Gemini CLI do not support Claude Code hooks. The quality rule (`.claude/rules/context-quality.md`) is also Claude Code-specific.

Cross-tool features like skills (`.claude/skills/`) and AGENTS.md work in OpenCode and Codex CLI without Context Guard.

## Components

### Hook: context-drift-check.sh

- **Event:** PostToolUse on `Bash` (filters for `git commit` commands)
- **Fires:** After a successful git commit
- **Checks:**
  1. Compares each context file's last-modified commit vs the most recent source-code commit
  2. Detects broken file-path references inside context files
  3. Flags when `package.json` or `pyproject.toml` changed more recently than context files
- **Output:** Lists stale files and recommends `/ai-context audit`, or stays silent if everything is current
- **Throttle:** Max once per hour via `.git/.context-guard-last-check` timestamp

### Hook: context-structural-change.sh

- **Event:** PostToolUse on `Write|Edit`
- **Fires:** After creating or editing structural files (commands, skills, agents, rules, manifests, config)
- **Reminds:** Which context files may need updating based on the type of change
- **File patterns:**
  - `commands/*.md` → AGENTS.md, CLAUDE.md, llms.txt
  - `.claude/skills/*/SKILL.md` → AGENTS.md, CLAUDE.md, llms.txt
  - `.claude/agents/*.md` → AGENTS.md
  - `.claude/rules/*.md` → CLAUDE.md, AGENTS.md
  - `package.json`, `pyproject.toml`, config files → all context files

### Rule: context-quality.md

Auto-loaded every session. Establishes cross-file consistency, path verification, version accuracy, command accuracy, and a sync-points table mapping project changes to context files.

## Installation

The `/context-guard install` command:

1. Copies hook scripts to `.claude/hooks/` in the target project
2. Merges hook configuration into `.claude/settings.json`
3. Copies the quality rule to `.claude/rules/context-quality.md`
4. Makes hook scripts executable

### Settings.json Configuration

```json
{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Bash",
        "hooks": [{
          "type": "command",
          "command": ".claude/hooks/context-drift-check.sh"
        }]
      },
      {
        "matcher": "Write|Edit",
        "hooks": [{
          "type": "command",
          "command": ".claude/hooks/context-structural-change.sh"
        }]
      }
    ]
  }
}
```

## Uninstallation

The `/context-guard uninstall` command removes the hook scripts, settings.json entries, and the quality rule.

## Customisation

### Throttle Interval

Edit `context-drift-check.sh` line with `3600` (seconds) to change the check interval. Set to `0` to check on every commit.

### File Patterns

Edit `context-structural-change.sh` case statement to add or remove structural file patterns.

## Troubleshooting

| Issue | Cause | Fix |
|-------|-------|-----|
| Hooks not firing | Scripts not executable | `chmod +x .claude/hooks/*.sh` |
| No output after commit | Throttle active | Delete `.git/.context-guard-last-check` to reset |
| "jq: command not found" | jq not installed | Install jq: `apt install jq` or `brew install jq` |
| Hook errors in logs | Wrong project directory | Check `CLAUDE_PROJECT_DIR` is set correctly |