A website works for me but not for one user

Someone reports that a page is broken, and it works every time you try. The difference is almost always in their browser, their settings or what their browser is sent. These tools let them show you that without installing anything or sharing their screen, and nothing they open here is sent to this site or anyone else. Send them the links, and ask them to paste back or attach what each one gives.

Take care with secrets. This runs only in your browser: what you enter isn't uploaded, stored or put in a link, and the page is built so that it can't send it anywhere else. Your browser's extensions and other software on your device can still see what's on screen, so use a device you trust and real secrets only when you need to. Disconnecting from the internet once the page has loaded gives the most protection. Use is at your own risk: see the terms.

1. Find out what they’re using

Ask them to open the User Agent Parser. It starts with their own browser’s details: the browser and version, the operating system and the kind of device. If they choose Copy a link to this input and send you the link, you see exactly what they see. In Chrome and Edge, This browser’s client hints adds the full version.

Then try the page in the same browser yourself. An old version, a phone, or an in-app browser (a link opened inside an email or social app) explains many reports on its own. The string can’t tell everything: every Mac browser reports macOS 10.15.7, and Windows 10 and 11 look the same, so ask them if it matters.

2. Compare their settings with yours

Next, ask them to open What Your Browser Reveals, choose Copy all and paste the text into their reply. Open it yourself and compare. The rows that most often explain “works for me”:

• Time zone, Languages and Number and date format: dates a day out, prices in the wrong format, or a form that rejects 23/10/2026 because it expects 10/23/2026.
• Window and Pixel ratio: a small window or high zoom can push a button off screen or switch the page to its phone layout.
• Cookies allowed, Global Privacy Control and Do Not Track: blocked cookies break sign-ins and carts; a privacy setting or extension may block a script the page needs.
• Dark mode, Reduce motion and More contrast: a page styled for one can hide text or controls in the other.

To test a difference, change your own setting to match theirs, or set your computer’s time zone or language to theirs for a moment.

3. See what they see

A recording beats a description. On a computer, they can open the Screen Recorder, choose Start recording, share the tab or window with the problem, go through the steps, then Stop and Save the video to send you. Screen recording works in desktop browsers only; on a phone, the phone’s own screen recording does the same. Ask them to close anything private first, as everything on the shared screen is recorded.

4. Capture what their browser asked for and got

If the page fails rather than looks wrong, the cause is often in a request: a 403 for them, a blocked script, or a slow call that times out. Ask them to open their browser’s developer tools at the Network tab, reproduce the problem, then right-click in the list of requests and save all as HAR (Debugging a failing API call has the details).

A HAR holds their cookies and sign-in tokens. Ask them to open it in the HAR Viewer first and send you the copy from Save the redacted HAR, never the original. Open that copy in the HAR Viewer yourself: failed requests are in red, and Filter narrows the list to the address that matters.

5. If a key or shortcut doesn’t work for them

When typing, a shortcut or a game control fails for one person, their keyboard layout is a likely cause: on a French, German or other layout, the same physical key gives a different character, and some characters need AltGr. Ask them to press the key in Key Codes and tell you event.key and event.code. Code that checks event.key for a character, or event.code for a position, behaves differently on different layouts; the line of code it shows is a starting point for a fix.