No. A robots.txt file applies only to the exact host, protocol and port where it is served. Rules on www.example.com do not cover blog.example.com, and a file on http does not govern https. Every subdomain you want to control needs its own robots.txt at its own root.
What counts as a separate site
- www.example.com and example.com are different hosts.
- shop.example.com is a different host from the main domain.
- http and https versions are treated separately.
- A non-standard port is its own origin.
Why this causes problems
A staging subdomain with no rules can be crawled and indexed, and a blog subdomain may lack the restrictions you set on the main site. Teams often fix the main file and forget the others.
Not sure if this is hurting your site?
Get the fixes that matter most, in priority order.
How to manage several files
- List every host and subdomain that serves public pages.
- Open /robots.txt on each one and read it.
- Create a file where one is missing, using the robots.txt generator.
- Check each with the tester.
Keep one version of your site
Redirect alternate versions, such as http to https and non-www to www, to a single preferred address so only one robots.txt matters. Check redirects with the redirect checker.
Subdomain or subfolder?
This is one reason many sites prefer subfolders: one file, one set of rules. I compare the options in ccTLD vs subfolder vs subdomain.
Protect staging properly
Do not rely on robots.txt to hide a staging site, because blocked URLs can still appear in results through links. Use password protection, as explained in noindex vs canonical vs robots.txt.
Frequently asked questions
Can one file cover all my subdomains?
No. Each subdomain needs its own file.
What about a file in a subfolder?
It is ignored. The file must sit at the root of the host.
Next steps
If you run several subdomains and want them checked, contact me here.
More in this series (robots.txt testing questions): start with Robots.txt Tester and AI Crawler Checker, then explore:
- How to Test Robots.txt in Google Search Console
- Robots.txt Returns 404 or 500: What Google Does and How to Fix It
- How to Block Images From Google With Robots.txt
- Robots.txt User-Agent Groups: Which Rules Does Googlebot Follow?
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