Hooks / formatting

rustfmt after Rust edit

Runs rustfmt on Rust files after Claude edits them.

What it does

Gates on .rs files and runs rustfmt on the edited file only, so large workspaces stay fast.

When it runs

Config

Merge this into .claude/settings.json - or use the generator to combine hooks.

{
  "hooks": {
    "PostToolUse": [
      {
        "hooks": [
          {
            "type": "command",
            "command": "${CLAUDE_PROJECT_DIR}/.claude/hooks/rustfmt-after-edit.sh",
            "timeout": 30
          }
        ],
        "matcher": "Edit|Write"
      }
    ]
  }
}

Script

Save as .claude/hooks/rustfmt-after-edit.sh and chmod +x it.

#!/bin/bash
# rustfmt-after-edit: run after Claude edits a file. Reads hook JSON from stdin.
set -u
file=$(jq -r '.tool_input.file_path // empty')
[ -z "$file" ] && exit 0
[ -f "$file" ] || exit 0
case "$file" in
*.rs) ;;
  *) exit 0 ;;
esac
if ! command -v rustfmt >/dev/null 2>&1; then
  exit 0  # formatter not installed; stay silent
fi
rustfmt "$file" >/dev/null 2>&1
exit 0

Install

1. Save the script to .claude/hooks/rustfmt-after-edit.sh and run: chmod +x .claude/hooks/rustfmt-after-edit.sh
2. Install the formatter (rustfmt) and make sure it is on your PATH, plus jq.
3. Add the config fragment to .claude/settings.json (or use the generator).

Test it

• Positive: ask Claude to edit a matching file (*.rs), then check the file was reformatted.
• Negative: ask Claude to edit a non-matching file (e.g. README.txt) - the formatter should not run (check with /doctor or debug logs).

Sources

• Claude Code hooks reference (checked 2026-09-10)
• Claude Code hooks guide (checked 2026-09-10)