What are HTTP status codes?

HTTP status codes are three-digit numbers returned by a web server to indicate the result of a client's request. They are grouped into five classes: 1xx (Informational), 2xx (Success), 3xx (Redirection), 4xx (Client Error), and 5xx (Server Error). For example, 200 means the request succeeded, 404 means the resource was not found, and 500 means the server encountered an error.

What is the difference between 301 and 302 redirects?

A 301 redirect means the resource has permanently moved to a new URL — search engines will update their index to the new URL and pass link equity. A 302 redirect means the resource is temporarily at a different URL — search engines keep the original URL indexed. Use 301 for permanent URL changes (domain migration, restructuring) and 302 for temporary situations (maintenance, A/B testing).

What is the difference between 401 and 403?

401 Unauthorized means the client has not provided valid authentication credentials — the request can be retried with proper credentials (e.g., a login token). 403 Forbidden means the server understood the request and the client may be authenticated, but the client does not have permission to access the resource. Re-authenticating will not help with a 403.

What is the difference between 404 and 410?

404 Not Found means the server cannot find the resource — it may exist in the future or the URL may be wrong. 410 Gone means the resource previously existed but has been intentionally and permanently removed. Search engines treat 410 as a stronger signal to deindex the page compared to 404.

What causes a 502 Bad Gateway error?

A 502 Bad Gateway error occurs when a server acting as a gateway or proxy (like Nginx or a load balancer) receives an invalid or no response from the upstream backend server. Common causes include: the backend application crashed, the backend is overloaded and not responding, network issues between the proxy and backend, or misconfigured proxy settings.

What should I do when I get a 429 Too Many Requests error?

A 429 error means you have exceeded the API's rate limit. Check the Retry-After response header for how long to wait before retrying. Implement exponential backoff in your code — wait 1s, then 2s, then 4s between retries. Consider caching responses, reducing request frequency, or upgrading to a higher API tier if available.

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HTTP Status Code Reference

HTTP status codes indicate the result of server requests. Categories: 1xx (informational), 2xx (success), 3xx (redirect), 4xx (client error), 5xx (server error). Common codes: 200 (OK - success), 201 (Created), 204 (No Content), 301 (Moved Permanently - permanent redirect), 302 (Found - temporary redirect), 304 (Not Modified - cached), 400 (Bad Request - invalid syntax), 401 (Unauthorized - auth required), 403 (Forbidden - no permission), 404 (Not Found), 429 (Too Many Requests - rate limited), 500 (Internal Server Error), 502 (Bad Gateway), 503 (Service Unavailable). Use in API design, debugging, and web development.

Complete reference of all HTTP status codes (1xx–5xx). Search and filter by category, view descriptions and common use cases, and copy code + message instantly. Color-coded by category with highlighted common codes.

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Showing 61 status codes

100Continue1xx Informational

The server has received the request headers and the client should proceed to send the request body.

Use case: Large file uploads where the client checks if the server will accept the request before sending the body.

101Switching Protocols1xx Informational

The server is switching protocols as requested by the client via the Upgrade header.

Use case: Upgrading an HTTP connection to WebSocket (ws://) for real-time communication.

102Processing1xx Informational

The server has received and is processing the request, but no response is available yet.

Use case: Long-running WebDAV operations where the server needs to prevent the client from timing out.

103Early Hints1xx Informational

Used to return response headers before the final HTTP message, allowing the browser to preload resources.

Use case: Sending Link headers early so the browser can start loading CSS and JS while the server prepares the full response.

200OK★ Common2xx Success

The request has succeeded. The meaning depends on the HTTP method used.

Use case: Standard successful GET response returning requested data, or successful POST/PUT operation.

201Created2xx Success

The request has been fulfilled and a new resource has been created.

Use case: REST API response after successfully creating a new user, post, or any resource via POST.

202Accepted2xx Success

The request has been accepted for processing, but the processing has not been completed.

Use case: Async job queues — the server acknowledges receipt but will process the task later (e.g., video encoding).

203Non-Authoritative Information2xx Success

The returned metadata is not from the origin server but from a local or third-party copy.

Use case: Proxy servers returning cached or transformed response headers that differ from the origin.

204No Content2xx Success

The server has fulfilled the request but does not need to return a body.

Use case: Successful DELETE requests or form submissions where no response body is needed.

205Reset Content2xx Success

The server fulfilled the request and asks the client to reset the document view.

Use case: After a form submission, telling the browser to clear the form fields.

206Partial Content2xx Success

The server is delivering only part of the resource due to a Range header sent by the client.

Use case: Video streaming and resumable file downloads where only a portion of the file is requested.

207Multi-Status2xx Success

Conveys information about multiple resources in situations where multiple status codes might be appropriate.

Use case: WebDAV batch operations where each sub-request may have a different result.

208Already Reported2xx Success

Used inside a DAV: propstat response to avoid repeatedly enumerating internal members of multiple bindings.

Use case: WebDAV responses to prevent listing the same resource multiple times in recursive operations.

226IM Used2xx Success

The server has fulfilled a GET request and the response is a representation of the result of instance-manipulations applied to the current instance.

Use case: Delta encoding where only the changes since the last request are sent to save bandwidth.

300Multiple Choices3xx Redirection

The request has more than one possible response and the user or user agent should choose one.

Use case: Content negotiation where multiple formats (HTML, JSON, XML) are available for the same resource.

301Moved Permanently★ Common3xx Redirection

The requested resource has been permanently moved to a new URL. Search engines update their index.

Use case: Domain migration (old-site.com → new-site.com) or permanently changing URL structure. SEO-friendly redirect.

302Found★ Common3xx Redirection

The requested resource temporarily resides at a different URL. The client should continue using the original URL.

Use case: Temporary redirects during maintenance, A/B testing, or redirecting after form submission (PRG pattern).

303See Other3xx Redirection

The response to the request can be found at another URL using a GET method.

Use case: Redirecting after a POST request to a GET page (Post/Redirect/Get pattern) to prevent form resubmission.

304Not Modified3xx Redirection

The resource has not been modified since the last request. The client can use the cached version.

Use case: Browser caching — the server confirms the cached version is still valid, saving bandwidth.

307Temporary Redirect3xx Redirection

The request should be repeated with another URL, but future requests should still use the original URL. The method and body are not changed.

Use case: HTTPS enforcement — redirecting HTTP to HTTPS while preserving the request method (POST stays POST).

308Permanent Redirect3xx Redirection

The resource has been permanently moved. Like 301 but the method and body are not changed.

Use case: Permanent URL changes for APIs where POST requests must be preserved (unlike 301 which may change to GET).

400Bad Request★ Common4xx Client Error

The server cannot process the request due to a client error such as malformed syntax or invalid parameters.

Use case: Invalid JSON in request body, missing required fields, or invalid query parameters in API calls.

401Unauthorized★ Common4xx Client Error

The request requires user authentication. The client must include valid credentials.

Use case: Accessing a protected API endpoint without a valid JWT token or API key.

402Payment Required4xx Client Error

Reserved for future use. Originally intended for digital payment systems.

Use case: Some APIs use this for exceeded free tier limits or when a paid subscription is required.

403Forbidden★ Common4xx Client Error

The server understood the request but refuses to authorize it. Authentication will not help.

Use case: A logged-in user trying to access admin-only resources, or IP-blocked requests.

404Not Found★ Common4xx Client Error

The server cannot find the requested resource. The URL is not recognized.

Use case: Accessing a deleted page, mistyped URL, or requesting a resource that does not exist.

405Method Not Allowed4xx Client Error

The HTTP method used is not supported for the requested resource.

Use case: Sending a DELETE request to an endpoint that only accepts GET and POST.

406Not Acceptable4xx Client Error

The server cannot produce a response matching the Accept headers sent by the client.

Use case: Requesting application/xml from an API that only serves application/json.

407Proxy Authentication Required4xx Client Error

The client must first authenticate with the proxy server.

Use case: Corporate network proxies that require user login before allowing internet access.

408Request Timeout4xx Client Error

The server timed out waiting for the request from the client.

Use case: Slow client connections where the server closes the idle connection after a timeout period.

409Conflict4xx Client Error

The request conflicts with the current state of the server resource.

Use case: Trying to create a user with an email that already exists, or editing a resource that was modified concurrently.

410Gone4xx Client Error

The resource is no longer available and will not be available again. Unlike 404, this is permanent.

Use case: Deliberately removed content (discontinued product, deleted account) — tells search engines to deindex.

411Length Required4xx Client Error

The server requires the Content-Length header to be specified in the request.

Use case: File upload endpoints that need to know the request body size before accepting it.

412Precondition Failed4xx Client Error

One or more conditions in the request header fields evaluated to false.

Use case: Conditional requests with If-Match or If-Unmodified-Since headers that fail (optimistic concurrency control).

413Content Too Large4xx Client Error

The request body is larger than the server is willing or able to process.

Use case: Uploading a file that exceeds the server's maximum upload size limit (e.g., > 10 MB).

414URI Too Long4xx Client Error

The URI provided in the request is too long for the server to process.

Use case: Extremely long query strings, often from improperly encoded data being passed via GET instead of POST.

415Unsupported Media Type4xx Client Error

The server refuses the request because the payload format is not supported.

Use case: Sending XML to an endpoint that only accepts JSON, or uploading a .exe to an image upload endpoint.

416Range Not Satisfiable4xx Client Error

The range specified in the Range header cannot be fulfilled.

Use case: Requesting byte range 1000-2000 of a file that is only 500 bytes long.

417Expectation Failed4xx Client Error

The expectation given in the Expect request header could not be met by the server.

Use case: Server rejecting an Expect: 100-continue header because it cannot handle the expected request.

418I'm a Teapot4xx Client Error

An April Fools' joke from RFC 2324. The server refuses to brew coffee because it is a teapot.

Use case: Easter egg in APIs and web servers. Sometimes used as a humorous rejection or to indicate a deliberately unsupported request.

421Misdirected Request4xx Client Error

The request was directed at a server that is not able to produce a response.

Use case: HTTP/2 connection coalescing where a request is sent to a server that doesn't serve that domain.

422Unprocessable Content4xx Client Error

The server understands the content type and syntax but cannot process the contained instructions.

Use case: Valid JSON with semantic errors — e.g., an age field set to -5 or a date in the past for a future event.

423Locked4xx Client Error

The resource that is being accessed is locked.

Use case: WebDAV file locking — another user has the document checked out for editing.

424Failed Dependency4xx Client Error

The request failed because it depended on another request that also failed.

Use case: Batch operations where a later step depends on an earlier one that failed.

425Too Early4xx Client Error

The server is unwilling to process a request that might be replayed.

Use case: TLS 1.3 early data (0-RTT) where the server rejects potentially replayed requests for safety.

426Upgrade Required4xx Client Error

The server refuses to perform the request using the current protocol but might after the client upgrades.

Use case: Server requiring the client to switch from HTTP/1.1 to HTTP/2, or to use TLS.

428Precondition Required4xx Client Error

The server requires the request to be conditional to prevent lost updates.

Use case: API requiring If-Match header for PUT requests to prevent overwriting concurrent changes.

429Too Many Requests4xx Client Error

The user has sent too many requests in a given amount of time (rate limiting).

Use case: API rate limiting — e.g., exceeding 100 requests per minute. Check Retry-After header for wait time.

431Request Header Fields Too Large4xx Client Error

The server refuses the request because the header fields are too large.

Use case: Excessive cookies or very long authorization tokens causing request headers to exceed server limits.

451Unavailable For Legal Reasons4xx Client Error

The resource is unavailable due to legal demands such as government censorship or court order.

Use case: Content blocked due to DMCA takedown, GDPR compliance, or government-ordered censorship.

500Internal Server Error★ Common5xx Server Error

The server encountered an unexpected condition that prevented it from fulfilling the request.

Use case: Unhandled exceptions, null pointer errors, database connection failures, or any unexpected server-side bug.

501Not Implemented5xx Server Error

The server does not support the functionality required to fulfill the request.

Use case: Server receiving an HTTP method it doesn't recognize (e.g., PATCH on a server that only supports GET/POST).

502Bad Gateway★ Common5xx Server Error

The server, acting as a gateway or proxy, received an invalid response from the upstream server.

Use case: Nginx or a load balancer receiving a bad response from a crashed backend application server.

503Service Unavailable★ Common5xx Server Error

The server is not ready to handle the request, usually due to maintenance or overload.

Use case: Planned maintenance windows, server overload during traffic spikes, or deployment in progress.

504Gateway Timeout5xx Server Error

The server, acting as a gateway or proxy, did not receive a timely response from the upstream server.

Use case: A slow database query causing the backend to exceed the proxy's timeout (e.g., Nginx 60s default).

505HTTP Version Not Supported5xx Server Error

The HTTP version used in the request is not supported by the server.

Use case: Client sending an HTTP/3 request to a server that only supports HTTP/1.1 and HTTP/2.

506Variant Also Negotiates5xx Server Error

The server has an internal configuration error: the chosen variant resource is configured to engage in content negotiation itself.

Use case: Misconfigured content negotiation where the selected resource creates a circular reference.

507Insufficient Storage5xx Server Error

The server is unable to store the representation needed to complete the request.

Use case: WebDAV server running out of disk space while trying to save an uploaded file.

508Loop Detected5xx Server Error

The server detected an infinite loop while processing the request.

Use case: WebDAV operations with circular symbolic links or recursive directory bindings.

510Not Extended5xx Server Error

Further extensions to the request are required for the server to fulfill it.

Use case: Server requiring additional HTTP extensions that the client did not provide.

511Network Authentication Required5xx Server Error

The client needs to authenticate to gain network access, typically for captive portals.

Use case: Hotel/airport WiFi login pages that intercept HTTP requests until the user signs in.

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Frequently Asked Questions

What are HTTP status codes?: HTTP status codes are three-digit numbers returned by a web server to indicate the result of a client's request. They are grouped into five classes: 1xx (Informational), 2xx (Success), 3xx (Redirection), 4xx (Client Error), and 5xx (Server Error). For example, 200 means the request succeeded, 404 means the resource was not found, and 500 means the server encountered an error.
What is the difference between 301 and 302 redirects?: A 301 redirect means the resource has permanently moved to a new URL — search engines will update their index to the new URL and pass link equity. A 302 redirect means the resource is temporarily at a different URL — search engines keep the original URL indexed. Use 301 for permanent URL changes (domain migration, restructuring) and 302 for temporary situations (maintenance, A/B testing).
What is the difference between 401 and 403?: 401 Unauthorized means the client has not provided valid authentication credentials — the request can be retried with proper credentials (e.g., a login token). 403 Forbidden means the server understood the request and the client may be authenticated, but the client does not have permission to access the resource. Re-authenticating will not help with a 403.
What is the difference between 404 and 410?: 404 Not Found means the server cannot find the resource — it may exist in the future or the URL may be wrong. 410 Gone means the resource previously existed but has been intentionally and permanently removed. Search engines treat 410 as a stronger signal to deindex the page compared to 404.
What causes a 502 Bad Gateway error?: A 502 Bad Gateway error occurs when a server acting as a gateway or proxy (like Nginx or a load balancer) receives an invalid or no response from the upstream backend server. Common causes include: the backend application crashed, the backend is overloaded and not responding, network issues between the proxy and backend, or misconfigured proxy settings.
What should I do when I get a 429 Too Many Requests error?: A 429 error means you have exceeded the API's rate limit. Check the Retry-After response header for how long to wait before retrying. Implement exponential backoff in your code — wait 1s, then 2s, then 4s between retries. Consider caching responses, reducing request frequency, or upgrading to a higher API tier if available.

HTTP Status Code Reference

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