PageKiwi Guide
400 Bad Request error
Facts checked Oct 8, 2026
A 400 Bad Request error means the website couldn't read what your browser sent it. Most often, clearing that one site's cookies fixes it.
What you'll see
- Chrome
- This page isn't working, then If the problem continues, contact the site owner. and HTTP ERROR 400 at the bottom.
- HTTP ERROR 431
- The same problem with a different number: the "headers" your browser sent (the notes that travel with every request, cookies included) are too big for the site.
- The site's own page
- 400 Bad Request with Request Header Or Cookie Too Large underneath, or Your browser sent a request that this server could not understand. Some add Size of a request header field exceeds server limit.
A different number? See 401 Unauthorized and 429 Too Many Requests, 403 Forbidden, 404 Page Not Found or 500 Internal Server Error.
If you're visiting a site
- Check the address. A typo, a space or a stray % sign in a pasted link can cause a 400. Go to the site's home page and find the page from there.
- Load the page again. You'll need to sign in to that site again, but nothing else changes.
- Still there? Try a private (incognito) window. If it works there, it's something saved in your browser: clear your cache as well.
- If it fails everywhere, on every device, the site needs fixing. Tell the business, with the time it happened.
Clearing cookies doesn't switch them off. If the site then won't keep you signed in, check that you haven't turned cookies off for it.
Stuck, and someone's helping you? Send them your details with My setup.
"Request Header Or Cookie Too Large"
This one is almost always about cookies. Your browser has saved more of them for that site than its server will read, so it turns every page away. It isn't a virus and it isn't your internet. Clear the site's cookies with the steps above and it goes away, until the pile builds up again.
If it's your site
- One visitor? Ask them to clear your site's cookies (send them this page).
- Lots of visitors, with "Cookie Too Large"? Something on your site is saving too many cookies, or too big ones. Think about what you added just before it started: a plugin, a chat box, a sign-up form, a tracking or ad tool. Your web person can find which cookies grow, and your host can raise the size limit while that's fixed.
- A 400 on one form or one link usually means the address or the form sends something the server can't read. Your web person can see the details in the server's error log.
Link Check reports any link on your pages that answers with a 400 as a dead link, and Site health shows what your home page answers. Neither sends your visitors' cookies, so a cookie problem won't show up there: ask someone who has it to try a private window.
Send this to your web person
Not sure what to say? Copy this into an email, add your website's address, and send it.
Hi, People are getting a 400 Bad Request error on [your website address], on [the page, or every page]. [The page says "Request Header Or Cookie Too Large".] It started around [the date and time]. Clearing the site's cookies fixes it for a while. Could you find which cookies our site saves that keep growing, and what added them? If it's quicker, could the host raise the header size limit while that's fixed? Please tell me what you changed. Thanks