All tools
Discovery
Subdomain Finder
Discover subdomains via certificate transparency and DNS bruteforce. Highlights mail subdomains and ESP CNAMEs.
This tool is being wired up. The analyzer ships in the next build phase.
About this check
Discover subdomains and identify mail-sending services.
Frequently asked questions
- What does the Subdomain Finder actually check?
- Discover subdomains and identify mail-sending services.
- Is this really free?
- Yes. Every on.bo tool is free, no signup required, no rate-limit tricks.
- Do you store the data I check?
- We log minimal metadata to keep the service healthy. Lookups themselves are not retained beyond short-term caching.