How to change the User-Agent in Chrome

You want to see the mobile version of a site, check how your server handles a crawler, or reproduce a bug a user reported from another browser. Each of these needs Chrome to send a different User-Agent. Which method fits depends on how long you need it and on which sites.

1. DevTools, for one tab

1. Open DevTools (Cmd+Option+I on a Mac, Ctrl+Shift+I on Windows and Linux).
2. Open the ⋮ menu, then More tools > Network conditions.
3. Under User agent, untick Use browser default and pick a browser from the list, or type your own string.

It changes both the header and navigator.userAgent, but only in that tab and only while DevTools stays open (Chrome DevTools docs). For a phone, device mode (the phone-and-tablet icon in DevTools) also sets the screen size and touch.

2. A launch flag, for a whole session

Chrome accepts a --user-agent flag at startup, and every tab in that session uses it. Start it with a separate profile so your normal windows aren't affected. On a Mac:

open -na "Google Chrome" --args --user-data-dir=/tmp/ua-test --user-agent="Mozilla/5.0 (iPhone; CPU iPhone OS 18_0 like Mac OS X)"

Useful for an automated or one-off test, but awkward for everyday browsing.

3. An extension rule, for chosen sites

A header editor can set User-Agent on every request to the sites you pick, with no DevTools open, and keep it until you switch the rule off. In Headerlane:

1. Click New rule and type the host, such as m.example.com, or leave it empty for all sites.
2. Add a header named User-Agent and paste the string you want.
3. Click Allow it in the banner and confirm Chrome's prompt. The rule runs only on sites you've allowed.

An extension changes what the server receives, not what the page's scripts read: navigator.userAgent still reports Chrome. Chrome also sends client hints, so for a convincing mobile request set these too:

• Sec-CH-UA-Mobile: ?1
• Sec-CH-UA-Platform: "Android" (with the quotes)

Which one fits

• DevTools to look at one page as another device, including its layout.
• The launch flag for a test run where every request must carry the string.
• An extension when a server should see a different User-Agent for days, on some sites, while you browse normally.

For other headers, such as auth tokens or feature flags, see how to set request headers in Chrome.