The User-Agent header describes a client identity supplied with a request. A server may use it when choosing a response, and crawler configuration can use it when applying robots rules.
Changing the string is useful for controlled comparisons. It does not turn your browser or crawler into genuine Googlebot, and it does not reproduce every part of Google’s infrastructure or rendering environment.
Inspect the original request
Open Network, reload, and select the document request. In Request Headers, record the User-Agent value. Keep the URL, response, and test time with it.
Modern browsers may also supply client hints and other request information. A server’s variation logic may therefore use more than the classic User-Agent header. If the output differs unexpectedly, compare the relevant headers and cache behaviour with the development team.
Change browser conditions deliberately
Chrome’s Network conditions tools allow user-agent overrides. The device toolbar also controls viewport and device emulation options. Inspect the actual request after changing settings so you know which condition changed.
A narrow viewport with a desktop identity and a mobile identity at a wide viewport are different tests. Use a small matrix when investigating mobile and desktop parity: record viewport, identity, and the content received.
Compare the document response before examining layout. If the HTML is already different, investigate serving logic. If the HTML is the same but the interface changes, inspect CSS and script behaviour next.
Configure the crawler identity
Screaming Frog provides user-agent configuration. Choose the identity required by the investigation and retain it with the crawl record. Check which robots group applies and whether security rules allow the authorised test.
A crawler using a Googlebot-style string may receive different output from the server. That proves a response difference under your test conditions, not that Google’s real crawler received it.
Verify genuine bot traffic separately
When analysing server logs, a request claiming to be Googlebot needs verification if its identity matters to the conclusion. Google documents verification methods, including supported IP information and DNS-based checks.
A reverse lookup alone is insufficient if the corresponding forward verification is omitted. Follow the documented process rather than trusting the text label in a log entry.
Compare one variable at a time
Use the same URL, similar cache conditions, and the same relevant headers where possible. Record status, returned content, canonical, robots instructions, and any challenge page. Repeat unexplained differences before declaring an agent-specific defect.
For a response blocked by robots rules, use the robots.txt investigation. For current versus recorded Google output, use URL Inspection.
My crawl and indexing analysis service covers these request comparisons. A technical SEO audit can then determine whether the difference affects a single route, a mobile template, or a wider access rule.