Parse the file before it's written. Agents sometimes leave a bracket unclosed, mix up quotes or break JSON, and you only find out when something later fails, often far from the cause. A parser on your own machine can catch it at the moment of writing.
Agents write and edit files in pieces. An edit that looks fine on its own can leave the whole file broken: an unclosed block, a trailing comma in package.json, a string that never ends. Nothing complains until the file is used.
Check parses shell, Python, PowerShell and JavaScript files, and package.json, on your machine before they're written. A write that would leave a file that doesn't parse is stopped, and the agent gets the parser's own error. The same goes for code passed to node -e or python -c, or fed to node or python - through a heredoc.
JavaScript is judged by Node's own parser: .mjs and .cjs files always, and an existing .js file only when an edit breaks it in a way no dialect explains. A brand-new .js file isn't judged, because JSX, Flow and bundler code are also written as .js. File contents are never sent anywhere: the parsing happens on your machine.
100 free blocks, then A$0.10 for each action Check stops, from a prepaid balance. Allowed actions are always free. No subscription. Windows and Linux; macOS isn't supported yet. Get your key at the console, then run this in your own terminal:
npx @golproductions/check@latest --installOr add Check as a plugin for Claude Code, Gemini CLI, Copilot CLI or Codex: the guide. Everything Check checks, and what it lets through: What Check does.
100 free blocks. Get your GOL API Key at the console.