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

bash
# 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:

bash
--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:

bash
--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