typecheck-on-edit

typecheck-on-edit

A Claude Code hook that pairs with format-on-edit: after each edit it runs the type checker the project already has and, when errors exist, adds them to Claude's context so the next action is the fix.

• TypeScript: finds the nearest tsconfig.json above the edited file and runs the project's own node_modules/.bin/tsc --noEmit against it. Never a network fetch.
• Python: pyright from node_modules/.bin or on PATH, else mypy, on the edited file.
• Go: go vet on the file's package.
• Edited file first. Errors in the file Claude just touched lead the list; errors elsewhere (callers it broke) follow, up to 25 lines.
• Context, not a block. The edit already happened; the hook informs rather than rejects.
• Fails open. No checker, a crash, or a 60-second timeout means silence and exit 0.

Files

Activate it (required manual step)

Add this to .claude/settings.json (project) or ~/.claude/settings.json (global):

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write|MultiEdit",
        "hooks": [
          {
            "type": "command",
            "command": "node \"$CLAUDE_PROJECT_DIR/.claude/hooks/typecheck-on-edit/typecheck-on-edit.mjs\"",
            "timeout": 90
          }
        ]
      }
    ]
  }
}

Installing the workflow-hooks plugin from the dotclaude marketplace wires this automatically.

Verify it

printf 'export const n: number = "x";\n' > src/bad.ts
echo '{"tool_name":"Edit","tool_input":{"file_path":"'$PWD'/src/bad.ts"},"cwd":"'$PWD'"}' \
  | node .claude/hooks/typecheck-on-edit/typecheck-on-edit.mjs

You should see a JSON object whose additionalContext lists the TS2322 error.

Tune it

{
  "typecheckOnEdit": {
    "enabled": true,
    "timeoutMs": 60000,
    "maxLines": 25
  }
}

On a large TypeScript project a full tsc --noEmit can take longer than the default cap; raise timeoutMs (and the settings.json timeout) or use project references so the nearest tsconfig.json is a small one.

Hooks run arbitrary commands on your machine with your credentials whenever their event fires. Read any hook script (including this one) before enabling it.