HTTP 511 — Network Authentication Required
A 5xx server error: the server failed to fulfil an apparently valid request.
Network Authentication Required
The client must authenticate to gain network access.
What it means
The client needs to authenticate to gain network access — used by captive portals (e.g. public Wi-Fi login pages).
When to use it
Returned by captive portals to redirect to a login page.
Other 5xx codes
About HTTP Status Codes
This HTTP status codes directory covers every standard response code from the 1xx informational range through 5xx server errors. Each entry shows the numeric code, its canonical reason phrase and a one-line summary, and the whole list can be searched by number, name or meaning — 301, Unauthorized and timeout all find their targets — or filtered by response class.
Every code opens onto its own dedicated page with a full explainer: what the status actually means, when to use it in your own APIs and applications, whether responses with that code are cacheable by default, and the RFC that defines it. Related codes from the same class are linked at the bottom, so comparing 401 with 403 or 301 with 308 takes one click.
The five classes are the fastest mental model for reading any response: 1xx means the request is continuing, 2xx means success, 3xx means redirection, 4xx means the client made a mistake and 5xx means the server failed. The directory is organized around exactly that structure.
How to use HTTP Status Codes
- Type a code, a reason phrase or a keyword into the search box — for example 404, Not Found or redirect.
- Use the class filter to narrow the list to informational, success, redirection, client-error or server-error codes.
- Open any code’s page to read what it means, when to use it, its default cacheability and the defining RFC.
- Check the related-codes section to compare neighbors from the same class.
- Use the copy button to grab the code for a bug report, test or API spec.