Understanding HTTP Status Codes: The Complete Guide

HTTP status codes are standardized response codes issued by a server in response to a client’s request. They help both humans and machines understand what happened to an HTTP request — whether it succeeded, failed, or something in between. Let me refresh your understanding HTTP Status Codes: The Complete Guide here.

This guide breaks down HTTP status codes into their five broad categories and highlights the most commonly used ones.

📘 HTTP Status Code Categories

All HTTP status codes are three-digit integers, and the first digit indicates the general category of response:

Code Range	Category	Meaning
1xx	Informational	Request received, continuing
2xx	Success	Request successfully processed
3xx	Redirection	Further action required
4xx	Client Error	Request has bad syntax
5xx	Server Error	Server failed to fulfill request

✅ 2xx – Success

These indicate the request was received, understood, and accepted.

200 OK

• The request was successful.
• Common for GET or POST responses.

201 Created

• A new resource was created (often in response to a POST).
• Used in REST APIs when creating a new object.

204 No Content

• The request succeeded, but there’s no response body.
• Useful for DELETE or PUT operations.

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🚦 3xx – Redirection

These indicate that the client must take additional steps to complete the request.

301 Moved Permanently

• Resource has been permanently moved to a new URL.
• Browsers and clients should update bookmarks.

302 Found (Temporary Redirect)

• Resource is temporarily at another URL.

304 Not Modified

• The client can use cached data; nothing has changed since the last request.
• Often used with the If-Modified-Since header.

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⚠️ 4xx – Client Errors

These errors indicate that the client did something wrong.

400 Bad Request

• The server couldn’t understand the request due to malformed syntax.

401 Unauthorized

• Authentication is required but missing or invalid.
• Often paired with WWW-Authenticate header.

403 Forbidden

• Client is authenticated, but not authorized to access the resource.

404 Not Found

• The requested resource could not be found.

405 Method Not Allowed

• HTTP method not supported by the endpoint (e.g., PUT to a GET-only URL).

429 Too Many Requests

• Client has sent too many requests in a short time.
• Used for rate limiting.

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💥 5xx – Server Errors

These indicate the server failed to process a valid request.

500 Internal Server Error

• A generic error for unexpected conditions on the server.

502 Bad Gateway

• Received an invalid response from an upstream server (e.g., proxy error).

503 Service Unavailable

• Server is temporarily unavailable (e.g., overload or maintenance).

504 Gateway Timeout

• Server did not receive a timely response from the upstream service.

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🔐 Special Considerations

• Use consistent codes in your API design to improve debugging and DX.
• Leverage the right codes to enforce RESTful principles and best practices.
• Avoid using 200 OK for all responses — communicate meaning with precise codes.

📌 Summary Table

Code	Meaning	Use Case
200	OK	Successful GET, POST
201	Created	Resource created
204	No Content	Successful but no response body
301	Moved Permanently	URL changed, update client
302	Found (Temporary Redirect)	Temporary redirect
304	Not Modified	Use cached version
400	Bad Request	Invalid input or syntax
401	Unauthorized	Missing/invalid auth
403	Forbidden	Authenticated but not allowed
404	Not Found	Resource doesn’t exist
405	Method Not Allowed	HTTP verb not supported
429	Too Many Requests	Rate limiting
500	Internal Server Error	Unhandled server exception
502	Bad Gateway	Proxy/gateway upstream failure
503	Service Unavailable	Temporarily overloaded or down
504	Gateway Timeout	Upstream timeout

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🧪 Summary

HTTP status codes are standardized responses from a server that indicate the outcome of a client’s request—whether it succeeded, failed, or needs further action.