Test-on-Save Hook

Requires: Claude Code installed · A test or typecheck command

1. 1

   Add the hook to settings

   In `.claude/settings.json`, register a PostToolUse hook that runs after Edit/Write.

   jsonCopy

   {
     "hooks": {
       "PostToolUse": [
         {
           "matcher": "Edit|Write",
           "hooks": [{ "type": "command", "command": "npm run -s typecheck" }]
         }
       ]
     }
   }

2. 2

   Keep it fast

   Point the command at a quick check (typecheck or affected tests). The agent reads its output and fixes failures on the next turn.

You ask for a refactor and want it to stay green.

What to expect: After each edit the hook runs your typecheck; if it fails, Claude Code sees the errors and fixes them before moving on — you review a working result.

• Start with `typecheck`; graduate to `test -- --changed` once you trust the loop.