User-Agent String Builder
Build a custom User-Agent string from browser, OS and device details.
Constructing a user-agent
Sometimes you need a user-agent string that does not come from your own browser — for testing how a site responds to different browsers and devices, configuring a tool that identifies itself, or reproducing a specific client. This builds a correctly-formatted user-agent from the browser, operating system and device you specify, following the conventional structure those strings use.
Choose the components and the user-agent string is assembled.
For testing, on your own systems
The legitimate uses are testing and configuration: checking your own site serves the right thing to a mobile browser, setting the identifier for a script or bot you run, or reproducing a reported issue tied to a particular client. It pairs with a parser for the reverse job of decoding an existing string. Worth noting, as with parsing, that a user-agent can be set to anything, which is precisely why it must never be trusted as a security signal — it is a hint, freely changeable, useful for testing rather than trust.
Questions & answers
Why build a custom user-agent?
For testing how a site responds to different clients, configuring a tool's identifier, or reproducing an issue tied to a specific browser or device.
Can I set a user-agent to anything?
Yes — which is exactly why it must never be trusted as a security signal, only used as a freely-changeable hint.
Is anything uploaded?
No. The string is built in your browser.