|Your everyday productivity workspaceSearchable quick-reference for HTTP 1xx–5xx codes with practical context, common causes, and what to do.
Last updated: June 2026
100
Continue
Informational
The server has received the request headers and the client should proceed to send the body.
When you'll see this
Large file uploads or when the client wants to check if the server will accept a request before sending a large payload.
Common causes
What to do
Send the request body if you receive 100 Continue. Most browsers handle this automatically.
101
Switching Protocols
Informational
The server is switching protocols as requested by the client.
When you'll see this
WebSocket handshake upgrades from HTTP to WebSocket protocol.
Common causes
What to do
Expected during WebSocket setup — no action needed if upgrade succeeds.
200
OK
Success
The request succeeded.
When you'll see this
Successful GET, PUT, PATCH, or POST that returns data. The most common success response.
Common causes
What to do
Parse the response body. Check response.status === 200 before using data.
const res = await fetch('/api/users');
if (res.status === 200) { const data = await res.json(); }201
Created
Success
A new resource was successfully created.
When you'll see this
POST requests that create a new record — REST APIs return 201 with a Location header pointing to the new resource.
Common causes
What to do
Read the Location header for the new resource URL. Parse response body for the created object ID.
204
No Content
Success
The request succeeded but there is no response body.
When you'll see this
Successful DELETE requests or PUT/PATCH updates where no data needs to be returned.
Common causes
What to do
Do not call response.json() — there is no body. Treat as success if status is 204.
206
Partial Content
Success
The server is delivering only part of the resource due to a range request.
When you'll see this
Video streaming, resumable downloads, or byte-range requests on large files.
Common causes
What to do
Check Content-Range header. Combine chunks if building a full file client-side.
301
Moved Permanently
Redirect
The resource has permanently moved to a new URL.
When you'll see this
Old URLs redirected to new ones. Search engines transfer SEO authority to the new URL.
Common causes
What to do
Update your links to the new URL. Browsers cache 301 redirects — clear cache if testing.
302
Found
Redirect
The resource is temporarily at a different URL.
When you'll see this
Temporary redirects, login flows, or post-form redirects.
Common causes
What to do
Follow the Location header. Do not cache — the redirect is temporary.
304
Not Modified
Redirect
The cached version is still valid — no body is sent.
When you'll see this
Conditional GET requests with If-None-Match or If-Modified-Since headers.
Common causes
What to do
Use your cached copy. No network body to parse.
307
Temporary Redirect
Redirect
Temporary redirect that preserves the original HTTP method.
When you'll see this
API redirects where POST must stay POST (unlike 302 which may change to GET).
Common causes
What to do
Re-send the request to the Location URL with the same HTTP method.
308
Permanent Redirect
Redirect
Permanent redirect that preserves the original HTTP method.
When you'll see this
Permanent API endpoint moves where method must be preserved (POST stays POST).
Common causes
What to do
Update client code to use the new URL permanently. Method is preserved.
400
Bad Request
Client Error
The server cannot process the request due to a client error.
When you'll see this
Malformed JSON, missing required headers, invalid query parameters, or syntax errors in the request.
Common causes
What to do
Validate request format before sending. Read the error response body for specific field errors.
401
Unauthorized
Client Error
Authentication is required and has failed or not been provided.
When you'll see this
Missing or expired JWT/API token, not logged in, or invalid credentials.
Common causes
What to do
Check your auth token. Refresh the token or redirect to login. 401 = not authenticated.
// 401 = no valid token
if (res.status === 401) { redirectToLogin(); }403
Forbidden
Client Error
The server understood the request but refuses to authorize it.
When you'll see this
Logged in but lacking permission — wrong role, insufficient privileges, or resource access denied.
Common causes
What to do
Check user roles and permissions. 403 = authenticated but not authorized. Different from 401!
// 403 = authenticated but no permission
if (res.status === 403) { showAccessDenied(); }404
Not Found
Client Error
The requested resource does not exist.
When you'll see this
Wrong URL, deleted resource, typo in API path, or route not registered on the server.
Common causes
What to do
Verify the URL path and resource ID. Check if the resource was deleted or moved.
if (res.status === 404) { showNotFound(); }405
Method Not Allowed
Client Error
The HTTP method is not supported for this endpoint.
When you'll see this
Sending POST to a GET-only endpoint, or using DELETE where only PATCH is allowed.
Common causes
What to do
Check the Allow header for supported methods. Use the correct HTTP verb.
408
Request Timeout
Client Error
The server timed out waiting for the request.
When you'll see this
Slow client sending a large body, or server closed idle connection.
Common causes
What to do
Retry the request. For large uploads, use chunked transfer or resumable upload.
409
Conflict
Client Error
The request conflicts with the current state of the resource.
When you'll see this
Duplicate email on signup, version conflict on concurrent updates, or resource already exists.
Common causes
What to do
Read the conflict details. Refresh data and retry, or resolve the duplicate.
410
Gone
Client Error
The resource existed but has been permanently removed.
When you'll see this
Deliberately deleted content that should not return — stronger signal than 404 for SEO.
Common causes
What to do
Remove links to this resource. Unlike 404, 410 tells search engines to de-index.
413
Payload Too Large
Client Error
The request body exceeds the server's size limit.
When you'll see this
File uploads exceeding server limit, or POST body too large for API gateway.
Common causes
What to do
Reduce payload size, compress data, or use chunked/multipart upload.
414
URI Too Long
Client Error
The request URL exceeds the server's length limit.
When you'll see this
Too many query parameters, or excessively long GET URLs.
Common causes
What to do
Move data from query string to POST body. Shorten or paginate parameters.
415
Unsupported Media Type
Client Error
The request Content-Type is not supported by the server.
When you'll see this
Sending XML to a JSON-only API, or wrong Content-Type header on upload.
Common causes
What to do
Set Content-Type to what the API expects (usually application/json).
422
Unprocessable Entity
Client Error
The request is well-formed but contains semantic errors.
When you'll see this
Validation errors — valid JSON but business rules fail (negative age, invalid email format accepted by syntax but rejected by rules).
Common causes
What to do
Read validation errors in response body. Fix field values and resubmit.
429
Too Many Requests
Client Error
The client has sent too many requests in a given time period.
When you'll see this
API rate limiting, brute-force protection, or quota exceeded on third-party APIs.
Common causes
What to do
Check Retry-After header. Implement exponential backoff: wait 1s, 2s, 4s, 8s before retrying.
if (res.status === 429) {
const retryAfter = res.headers.get('Retry-After');
await sleep(retryAfter ? Number(retryAfter) * 1000 : 1000);
}500
Internal Server Error
Server Error
The server encountered an unexpected error.
When you'll see this
Unhandled exception in server code, database crash, or misconfiguration on the server side.
Common causes
What to do
Retry once. If persistent, check server logs. This is a server bug — not your fault as a client.
502
Bad Gateway
Server Error
The server acting as a gateway received an invalid response from upstream.
When you'll see this
Reverse proxy (nginx, Cloudflare) cannot reach the backend, or backend crashed mid-request.
Common causes
What to do
Retry after a delay. Check if the API service is up. Often transient during deployments.
503
Service Unavailable
Server Error
The server is temporarily unable to handle the request.
When you'll see this
Server overloaded, maintenance mode, or deliberate traffic shedding.
Common causes
What to do
Check Retry-After header. Implement retry with backoff. Show maintenance message to users.
504
Gateway Timeout
Server Error
The gateway did not receive a timely response from the upstream server.
When you'll see this
Backend took too long to respond — slow database query, long-running job, or network issue between proxy and app.
Common causes
What to do
Retry with backoff. Optimize slow endpoints. Consider async processing for long operations.
507
Insufficient Storage
Server Error
The server cannot store the representation needed to complete the request.
When you'll see this
WebDAV operations when disk is full, or storage quota exceeded on server.
Common causes
What to do
Contact server admin. Free up storage or increase quota.
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Our free HTTP Status Codes Reference covers 30+ standard codes from 1xx through 5xx with practical developer context.
Search by code number or keyword, filter by category, and see when you'll encounter each code, common causes, and what to do.
Includes code snippets for 200, 401, 403, 404, and 429. No signup required.
Read the full guide: HTTP status codes guide — all codes explained
Understand what 4xx and 5xx errors mean in your API responses.
Clarify authentication vs authorization errors.
Choose between 301, 302, 307, and 308.
Handle 429 Too Many Requests with backoff.
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