This generator builds a syntactically correct robots.txt from the choices you make: which crawlers a rule applies to, which paths to disallow or explicitly allow, an optional crawl delay, and the absolute URL of your sitemap. Getting the file right matters more than most people expect — a single stray 'Disallow: /' blocks an entire site, and it is one of the most common causes of a sudden traffic collapse after a launch. The other detail worth knowing is that robots.txt controls crawling, not indexing: a blocked URL can still appear in search results if other sites link to it, because Google never fetches the page to see your noindex tag. Use a meta robots noindex for pages that must stay out of the index.
Free, fast, and runs entirely in your browser — no signup, no upload to a server.