Google fetches robots.txt separately for every origin, which means example.com, www.example.com, and the https version can each be running different rules without anyone realizing it. TechySEO checks the actual file against your real URL inventory, catches the wildcard that's blocking more than intended, and flags the kind of mistake that took one well-known site weeks to recover from after a single stray Disallow: /.
Robots.txt is small, plain text, and easy to underestimate, which is exactly why it's caused some of the most dramatic SEO incidents on record. A single misplaced wildcard can take out entire sections of a site's crawl access in one edit. There's a well-known case of a site accidentally shipping a Disallow: / to production and watching itself disappear from Google over the following days, a mistake that took weeks to fully recover from once it was caught and fixed.
The subtler failures matter too. Block CSS and JavaScript and Google can't render the page the way a real visitor sees it, which affects how it evaluates content, page experience, and mobile usability all at once. Skip the Sitemap declaration and Googlebot has to find the sitemap some other way instead of being pointed straight at it.
Here's the part that catches people off guard: robots.txt is fetched per origin, not per site. https://example.com, https://www.example.com, and the plain HTTP version are each treated as separate origins with their own robots.txt. It's entirely possible for one to be configured correctly and another to still be running an old, more restrictive version nobody remembered to update.
A robots.txt file can be syntactically perfect and still be doing something nobody intended. Both get checked.
Check it against your real URLs, across every origin variant of your domain, before a wildcard you forgot about costs you a section of the site.
