/file-watcher

name: file-watcher
description: Chokidar-based file watcher that triggers `claude -p` on changes. Useful for automated AI reactions to file changes — design sync, code validation, config regeneration, etc.

File Watcher Skill

Overview

Sets up a file watcher using chokidar that monitors a path for changes and runs a Claude prompt against every changed file. The prompt supports a `{{file}}` placeholder that gets replaced with the changed file path.

Quick Start

# Watch src/ and analyze any changed file
node scripts/watch-files.mjs ./src 'Analyze {{file}} for issues'

# Watch only .tsx files with 1s debounce
node scripts/watch-files.mjs ./src 'Review {{file}} for React best practices' --glob '*.tsx' --debounce 1000

# Via package.json script (pass args after --)
bun run watch:files -- ./src 'Check {{file}}'

CLI Reference

node scripts/watch-files.mjs <path> <prompt> [--glob '<pattern>'] [--debounce <ms>]

| Arg | Required | Description | |-----|----------|-------------| | `<path>` | Yes | File or directory to watch | | `<prompt>` | Yes | Claude prompt. Use `{{file}}` for the changed file path | | `--glob` | No | Glob filter (e.g. `*.tsx`, `*.css`) | | `--debounce` | No | Debounce delay in milliseconds (default: 500) |

How It Works

1. Chokidar watches the target path for `add` and `change` events 2. Changes are debounced (default 500ms) to batch rapid saves 3. For each changed file, the `{{file}}` placeholder in the prompt is replaced with the actual file path 4. `claude -p '<prompt>' --print` is executed via `child_process.execSync` 5. Claude's output is logged to stdout

Example Prompts

| Use Case | Prompt | |----------|--------| | Code review | `'Review {{file}} for bugs and suggest fixes'` | | Type checking | `'Check {{file}} for TypeScript type issues'` | | Design sync | `'The design file {{file}} changed. Update the corresponding React component'` | | Test generation | `'Generate unit tests for {{file}}'` | | Documentation | `'Update documentation for changes in {{file}}'` |

Configuration

Glob Patterns

Filter which files trigger the watcher:

--glob '*.tsx'          # Only TypeScript React files
--glob '*.css'          # Only CSS files
--glob '*.{ts,tsx}'     # TypeScript files (not supported by chokidar glob — use without braces)

Debounce

Control how long to wait after the last change before triggering:

--debounce 200    # Fast (200ms) — good for single-file saves
--debounce 1000   # Slow (1s) — good for batch operations
--debounce 5000   # Very slow (5s) — good for build output directories

Troubleshooting

| Issue | Solution | |-------|----------| | `claude` CLI not found | Install Claude Code: `npm install -g @anthropic-ai/claude-code` | | Watcher not detecting changes | Check the path exists and you have read permissions | | Too many invocations | Increase `--debounce` value | | Prompt with special characters | Wrap prompt in single quotes; `{{file}}` is the only placeholder | | Permission denied | Ensure the watched directory is readable |

Dependencies

• `chokidar` (devDependency) — file system watcher
• `claude` CLI — must be installed globally and authenticated