HTTP Status Codes

Every HTTP status code with causes, retry advice and the ASP.NET Core way to return it.

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Common questions:
Codes

    What it does

    A reference you can search faster than you can type a search query. Every status code in the IANA registry (1xx to 5xx, from the current RFC 9110 and its extensions) is listed, plus widely seen unofficial codes such as nginx’s 499 Client Closed Request and Cloudflare’s 52x errors, clearly marked as unofficial.

    For each code you get:

    • Meaning and when to use it / common causes, written for people building and debugging APIs.
    • Cacheable by default: whether caches may store it without explicit Cache-Control (the RFC 9110 §15.1 list).
    • Retry guidance: safe to retry, retry after fixing something, or never, including how Polly and Microsoft.Extensions.Http.Resilience treat it.
    • ASP.NET Core: the TypedResults / Results call, the ControllerBase helper, the StatusCodes constant and the HttpStatusCode enum name, with gotchas such as the rate limiter rejecting with 503 unless configured, or IIS answering 404.13 for oversized uploads.
    • Specification: a link to the exact RFC section.

    How to use it

    Type a number (404), a prefix (42, 5xx) or words (timeout, redirect, upload). Filter by class, show only IANA codes, cacheable or retryable ones. Press Enter to open the first match and use the arrow keys in the list. Every code has its own link, for example /tools/http-status/#429, which opens and highlights it. Copy C# (or Ctrl+Enter) copies the snippet of the selected code; the filtered list exports as CSV or JSON.

    Privacy

    The reference is built into the page. Nothing you search for is sent anywhere; only your last search and filters are kept in local storage.