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typecheck-on-edit

PostToolUse hook that runs a quick typecheck for the file Claude just edited.

Trigger

  • Event: PostToolUse
  • Matcher: Edit|Write

What it does

  • .ts/.tsx → tsc --noEmit -p . --pretty false (only when tsconfig.json exists)
  • .py → mypy --no-color-output --hide-error-context <file>

Errors stream to stderr so Claude sees them as PostToolUse output.

Exit codes

Always 0. Type errors are surfaced as text, not as a block.

Kill switches

  • CLAUDE_HARNESSES_DISABLE=1

Notes

tsc runs in project mode (-p .) to honor the project's tsconfig.json and avoid spurious single-file errors. Without tsconfig.json, the hook skips TypeScript altogether.

Pack: verification-pack