Build a robots.txt with allow/disallow rules and a sitemap reference.
How it works
The generator writes directives in the standard robots.txt order: a single User-agent line, then a Disallow line for each path you list — or one bare "Disallow:" line if the field is left empty, which tells crawlers to allow everything — followed by any Allow overrides, an optional Crawl-delay, and a Sitemap URL on its own line at the end. The output textarea rewrites itself on every keystroke, so what you see is always the current state of the form.
FAQ
What does a blank Disallow field produce?
An explicit "Disallow:" line with nothing after the colon — that's the standard way of saying "allow everything," rather than omitting the directive entirely, which some crawlers could interpret differently.
Does Crawl-delay actually work on Google?
No — Google's crawler ignores Crawl-delay entirely (crawl rate is set in Search Console instead); Bing, Yahoo and several other crawlers do respect it, which is why the field is still here.
Free, unlimited, no account. If this saved you a paid tool, a small thanks is appreciated.