HTTP status code reference

A searchable list with plain-English meanings and when you will see each one.

FreeRuns in your browserNo signupUpdated 2026-10-29

SearchType a code such as 503, or a word such as redirect, cache, upload.Class

Matching

of 62 standard codes

Code

–

Narrow the search to one code

Rule of thumb: 2xx worked, 3xx look elsewhere, 4xx the request is wrong, 5xx the server is wrong. Registry last checked October 2026.

Status codes

100Informational
Continue
The server got the headers; send the body.
When you will see it: Large uploads that use Expect: 100-continue.
101Informational
Switching Protocols
The connection is changing protocol, usually to WebSocket.
When you will see it: Opening a WebSocket from a browser.
102Informational
Processing
WebDAV: the request is still being handled.
When you will see it: Rare; some WebDAV servers.
103Informational
Early Hints
Preload hints sent before the final response.
When you will see it: CDNs that push Link headers early for fonts and CSS.
200Success
OK
Success. The body holds the result.
When you will see it: Almost every normal page load and API read.
201Success
Created
A new resource now exists; Location says where.
When you will see it: POST to an API that creates an order or user.
202Success
Accepted
Received, will be processed later.
When you will see it: Queued jobs, email sending, batch imports.
203Success
Non-Authoritative Information
Success, but a proxy changed the response.
When you will see it: Transforming proxies; uncommon.
204Success
No Content
Success with an empty body.
When you will see it: DELETE requests, autosave pings, preflight handling.
205Success
Reset Content
Success; the client should reset its form.
When you will see it: Rare.
206Success
Partial Content
Only the requested byte range was sent.
When you will see it: Video streaming, resumable downloads.
207Success
Multi-Status
WebDAV: several results in one XML body.
When you will see it: WebDAV clients.
208Success
Already Reported
WebDAV: members already listed earlier.
When you will see it: WebDAV clients.
226Success
IM Used
Delta encoding was applied.
When you will see it: Very rare.
300Redirection
Multiple Choices
Several representations exist; pick one.
When you will see it: Rare; some content negotiation setups.
301Redirection
Moved Permanently
The URL has moved for good; update links.
When you will see it: Domain changes, http to https, old URLs after a redesign.
302Redirection
Found
Temporary redirect; keep using the original URL.
When you will see it: Login flows, A/B tests, short links. Many servers default to this.
303Redirection
See Other
Go GET this other URL.
When you will see it: After a form POST, to prevent resubmission.
304Redirection
Not Modified
Your cached copy is still current.
When you will see it: Browsers revalidating with ETag or If-Modified-Since.
305Redirection
Use Proxy
Deprecated.
When you will see it: Should never appear.
307Redirection
Temporary Redirect
Temporary redirect that keeps the method and body.
When you will see it: HSTS upgrades in the browser, API redirects.
308Redirection
Permanent Redirect
Permanent redirect that keeps the method and body.
When you will see it: Next.js and Vercel permanent redirects.
400Client error
Bad Request
The request is malformed or fails validation.
When you will see it: Bad JSON, missing fields, oversized headers.
401Client error
Unauthorized
Not authenticated; log in or send credentials.
When you will see it: Expired tokens, missing API keys.
402Client error
Payment Required
Reserved; some APIs use it for billing limits.
When you will see it: Payment gateways and metered APIs.
403Client error
Forbidden
Authenticated but not allowed.
When you will see it: Wrong role, blocked IP, WAF rules, directory listing disabled.
404Client error
Not Found
Nothing lives at this URL.
When you will see it: Deleted pages, typos in links, missing assets.
405Client error
Method Not Allowed
The URL exists but not for this verb.
When you will see it: POSTing to a page that only serves GET.
406Client error
Not Acceptable
Cannot produce a format the Accept header allows.
When you will see it: Strict content negotiation.
407Client error
Proxy Authentication Required
The proxy needs credentials.
When you will see it: Corporate networks.
408Client error
Request Timeout
The client took too long to send the request.
When you will see it: Slow mobile connections, half-open connections.
409Client error
Conflict
The request clashes with current state.
When you will see it: Duplicate usernames, editing a stale record.
410Client error
Gone
Removed on purpose and not coming back.
When you will see it: Retired pages; tells search engines to drop them faster than 404.
411Client error
Length Required
Content-Length header is missing.
When you will see it: Some proxies and uploads.
412Client error
Precondition Failed
An If-Match style condition failed.
When you will see it: Optimistic locking with ETags.
413Client error
Content Too Large
The body is bigger than the server allows.
When you will see it: File uploads over the nginx or PHP limit.
414Client error
URI Too Long
The URL is too long.
When you will see it: Huge query strings, GET where POST was meant.
415Client error
Unsupported Media Type
The body format is not supported.
When you will see it: Sending form data to a JSON-only API.
416Client error
Range Not Satisfiable
The byte range is outside the file.
When you will see it: Broken resumable downloads.
417Client error
Expectation Failed
The Expect header cannot be met.
When you will see it: Rare.
418Client error
I'm a teapot
An April Fools joke from RFC 2324.
When you will see it: Easter eggs and bot traps.
421Client error
Misdirected Request
Sent to a server that cannot answer for this host.
When you will see it: HTTP/2 connection reuse across domains.
422Client error
Unprocessable Content
Well-formed but semantically invalid.
When you will see it: Validation errors in Rails, Laravel and many APIs.
423Client error
Locked
WebDAV: the resource is locked.
When you will see it: WebDAV clients.
424Client error
Failed Dependency
WebDAV: an earlier request failed.
When you will see it: WebDAV clients.
425Client error
Too Early
Refusing a replayable early-data request.
When you will see it: TLS 1.3 0-RTT.
426Client error
Upgrade Required
Switch to a different protocol first.
When you will see it: Rare.
428Client error
Precondition Required
The request must be conditional.
When you will see it: APIs that force ETags to avoid lost updates.
429Client error
Too Many Requests
Rate limit hit; slow down.
When you will see it: API quotas, login brute-force protection, scrapers.
431Client error
Request Header Fields Too Large
Headers exceed the limit.
When you will see it: Cookie bloat, very large auth tokens.
451Client error
Unavailable For Legal Reasons
Blocked by a legal demand.
When you will see it: Geo-blocking for legal reasons.
500Server error
Internal Server Error
The server crashed or threw an unhandled error.
When you will see it: PHP fatal errors, uncaught exceptions, bad deploys.
501Server error
Not Implemented
The server does not support this method.
When you will see it: Unusual verbs on simple servers.
502Server error
Bad Gateway
The proxy got an invalid response upstream.
When you will see it: nginx in front of a crashed app, Cloudflare when origin fails.
503Server error
Service Unavailable
Temporarily down or overloaded.
When you will see it: Maintenance mode, traffic spikes, autoscaling lag.
504Server error
Gateway Timeout
The upstream took too long.
When you will see it: Slow database queries behind a proxy, serverless cold starts.
505Server error
HTTP Version Not Supported
The HTTP version is refused.
When you will see it: Rare.
506Server error
Variant Also Negotiates
Misconfigured content negotiation.
When you will see it: Very rare.
507Server error
Insufficient Storage
WebDAV: out of space.
When you will see it: WebDAV servers.
508Server error
Loop Detected
WebDAV: infinite loop in processing.
When you will see it: WebDAV servers.
510Server error
Not Extended
Further extensions are required.
When you will see it: Very rare.
511Server error
Network Authentication Required
Log in to the network first.
When you will see it: Hotel and airport Wi-Fi captive portals.

About this tool

How it works and how to read the result.

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What it does

This HTTP status codes list covers every standard code in the IANA registry with a one-line meaning and a note on where you are likely to meet it, so you can decode an error, a log line or a crawl report without reading an RFC. Type a code or a word such as "redirect", "cache" or "upload" and the list filters as you go. A class filter narrows the view to informational, success, redirection, client error or server error codes, and a copy button grabs the filtered list as plain text for a ticket or a message.

How to use it

Type the code you are seeing, for example 503, or a word from the problem.
Use the class filter to browse a whole group, such as all 4xx client errors.
Read the meaning, then the "when you will see it" line, which usually points at the real cause.
Copy the filtered list as plain text if you need to share it in a ticket, a pull request or a message.

How to read the result

Say a crawl report shows 1,240 pages returning 200, 38 returning 301, 12 returning 404 and 3 returning 500. The 200s are fine. The 301s are permanent redirects, which are expected after a URL change but worth checking for chains, where one redirect leads to another. The 404s are broken links to fix or redirect. The three 500s are the priority: the server failed on those pages, and users and search engines see nothing useful there.

The first digit sets the class. 2xx means the request worked. 3xx means look somewhere else, and the Location header says where. 4xx means the request itself was the problem: wrong URL, missing login, too many requests. 5xx means the server was the problem, which is the one group where the visitor did nothing wrong.

Codes outside the standard list, such as 499 from nginx or 520 to 527 from Cloudflare, are vendor-specific and will show "no match" here; look them up in that vendor's documentation.

Status codes are the first thing we check in a technical SEO audit. To generate the redirect rules that fix the 404s, use the redirect generator.

Questions

Frequently asked.

What is the difference between a 301 and a 302 redirect?

A 301 is permanent and tells browsers and search engines to update their records and pass ranking signals to the new URL. A 302 is temporary, so the old URL stays indexed. Use 301 or 308 for site moves and renamed pages, and 302 or 307 for short-lived switches such as a campaign or maintenance page.

What causes a 502 Bad Gateway?

A proxy such as nginx, a load balancer or Cloudflare could not get a valid response from the application behind it. Common causes are the app process having crashed, running out of memory, or a deploy that restarted it. Check the application logs first; the proxy is only the messenger.

Should a missing page return 404 or 410?

404 means not found, with no information about whether it ever existed. 410 means gone on purpose. Search engines treat 410 as a stronger signal and drop the URL faster. Use 410 for content you removed deliberately, and 404 for everything else. Either way, make sure the page does not return 200 with an error message.

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