Lint on save with Claude Code hooks

Claude Code runs shell commands at well-defined lifecycle points via the hooks config in ~/.claude/settings.json. The highest-leverage one is PostToolUse — it fires after any tool completes, so you can run a formatter or linter the moment a file is touched.

{
  "hooks": {
    "PostToolUse": [
      {
        "matcher": "Edit|Write|MultiEdit",
        "hooks": [
          {
            "type": "command",
            "command": "cd \"$CLAUDE_PROJECT_DIR\" && npx --yes eslint --fix \"$CLAUDE_FILE_PATH\" 2>/dev/null || true"
          }
        ]
      }
    ]
  }
}

Three things to notice:

• matcher is a regex over tool names — this fires only on file-mutating tools.
• The || true means lint failures don't block the tool output (hooks that exit non-zero are surfaced as errors to Claude).
• $CLAUDE_FILE_PATH and $CLAUDE_PROJECT_DIR are injected by the harness.

Project-scoped variant: put the same JSON in .claude/settings.json at the repo root and it applies only inside that repo.