format-on-edit

format-on-edit

A Claude Code hook that formats each file immediately after Claude edits or writes it, using whatever formatter the project itself has configured. No more "run the formatter" follow-ups or formatting-only cleanup commits at the end of a session.

• Project-driven detection. Formats with Biome when biome.json/biome.jsonc is present, otherwise Prettier when a Prettier config (or a prettier key in package.json) is present. Go, Rust, and Python files use gofmt, rustfmt, and ruff format respectively (ruff only when the project configures it).
• Local binaries only. JS-family formatters run from the project's node_modules/.bin; the hook never does a network npx fetch. If the binary is not installed, it silently does nothing.
• One file per event. Only the file Claude just touched is formatted, never the whole tree.
• Fails open. A missing, crashing, or hanging formatter (15-second cap) can never break the edit; the hook always exits 0.
• Zero dependencies. Node standard library only (node >= 18).

Files

After npx shadcn@latest add KhaledSaeed18/dotclaude/format-on-edit, both land in .claude/hooks/format-on-edit/.

Activate it (required manual step)

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

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

Installing the format-on-edit plugin from the dotclaude marketplace wires this automatically.

Verify it

# In a project with a Prettier or Biome config: write a mangled file, pipe the event, check it reformats
printf 'const   x=1\n' > src/messy.ts
echo '{"tool_name":"Write","tool_input":{"file_path":"'$PWD'/src/messy.ts"}}' \
  | node .claude/hooks/format-on-edit/format-on-edit.mjs
cat src/messy.ts

Tune it

• Add a formatter: extend formatFile() in the script with your tool; keep the pattern of detecting project config first and capping the run with a timeout.
• Restrict file types: edit the BIOME_EXTS / PRETTIER_EXTS sets.
• Formatter precedence: when both Biome and Prettier configs exist, Biome wins; reorder the checks in formatFile() to prefer Prettier.

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