4xx Client error
HTTP 431 Request Header Fields Too Large
The server won’t process the request because its header fields are too large, either one header on its own or all of them together.
Defined in RFC 6585, section 5(opens in a new tab)
//_01 Uptime checks
Is 431 up or down for a monitor?
Uptimecheck HTTP monitor
Default settings
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 431 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Is it down? checker
Free, at /is-it-down/
Up. The checker counts any answer below 500 as the site answering: a 431 comes from a server that is running.
//_02 Causes and fixes
Why you see 431 and what to do
Typical causes
- Cookies that have grown large over time.
- Very large authentication tokens or long referrer URLs.
If you run the site
- Keep cookies small, and check the header size limits of every proxy in the chain.
If you’re a visitor
- Clear the site’s cookies and try again.
Know the moment your site stops answering as it should
An Uptimecheck monitor requests your page as often as every minute, checks the status code against the ones you expect, confirms a failure with a second check and then alerts you.
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Questions
What does HTTP 431 mean?
The server won’t process the request because its header fields are too large, either one header on its own or all of them together.
Does an uptime monitor count 431 as down?
Down. It is outside the default 200–399 range, so a monitor reports an outage once a second check confirms it. If 431 is the answer you expect from that URL, add it to the monitor’s expected status codes.
Downtime is obsolete.
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