What Are HTTP Status Codes?

HTTP status codes are three-digit numbers returned by a web server in response to a client's request. They indicate whether the request was successful, redirected, or resulted in an error. Understanding these codes is essential for web development, API design, and debugging.

Status Code Categories

HTTP status codes are grouped into five categories based on the first digit:

1xx (Informational)

The request was received and the server is continuing to process it

2xx (Success)

The request was successfully received, understood, and accepted

3xx (Redirection)

Further action is needed to complete the request (usually a redirect)

4xx (Client Error)

The request contains an error on the client side

5xx (Server Error)

The server failed to fulfill a valid request

Who Uses This Tool?

This reference tool is designed for web developers, API developers, QA testers, and system administrators who need to quickly look up HTTP status codes, understand when to use each one, and compare similar codes.

How to Use This Tool

Browse by Category

All HTTP status codes are displayed in groups by their category (1xx through 5xx). Each group has a distinct color for easy identification. Simply scroll through the list to browse all codes.

Search for a Code

Use the search bar at the top to find a specific status code. You can search by:

Code number — Type "404" to find 404 Not Found
Name or keyword — Type "redirect" to find all redirection-related codes
Description keyword — Type "proxy" to find codes mentioning proxy servers

Filter by Category

Click the category tabs (All, 1xx, 2xx, 3xx, 4xx, 5xx) to show only codes from a specific group. This is useful when you know the general type of response but not the exact code.

View Details

Click on any status code card to expand it and see detailed information including:

Use Cases — Real-world scenarios when this code is returned
Common Headers — Response headers typically associated with this code
Related Codes — Similar or frequently confused codes for comparison

Pin Your Favorites

Click the bookmark icon on any code to pin it. Pinned codes appear at the top of the page for quick access. Your pins are saved in your browser and persist across sessions.

Features

Complete HTTP Status Code Reference

This tool covers all standard HTTP status codes defined in RFCs, including commonly used codes and less common ones.

200 OK, 301 Moved Permanently, 404 Not Found
500 Internal Server Error
103 Early Hints, 418 I'm a Teapot
451 Unavailable For Legal Reasons

Color-Coded Categories

Each category is visually distinguished with its own color scheme, making it easy to identify the type of response at a glance.

Informational codes are blue
Success codes are green
Redirection codes are amber
Client Error codes are red
Server Error codes are purple

Practical Use Cases

Every status code includes real-world use cases that explain when and why a server returns that specific code.

Choose the right status code for API design
Understand error responses when debugging
Learn best practices for HTTP responses

Commonly confused codes are linked together, allowing you to quickly navigate between them and understand the differences.

Compare 401 vs 403
Understand 301 vs 302 redirects
Differentiate 400 vs 422 errors

Pin and Quick Access

Bookmark your most-used status codes so they always appear at the top.

Pins saved locally in your browser
No account needed
Persistent across sessions

Pro Tip: Use the color-coded categories and pin feature together to create your personalized quick reference guide for the status codes you use most frequently in your projects.

Frequently Asked Questions

What is the difference between 401 and 403?

401 Unauthorized

Authentication Required

The client has not provided valid authentication credentials. The client should authenticate (log in) and retry.

User needs to log in
Missing or invalid credentials
Re-authenticating will solve the issue

403 Forbidden

Permission Denied

The client is authenticated but does not have permission to access the resource. Re-authenticating will not help.

User is logged in but lacks permission
Access is restricted by role or policy
Authentication won't solve the issue

When should I use 301 vs 302 redirect?

301 Moved Permanently

Permanent Redirect

Use when a resource has permanently moved to a new URL. Search engines will update their index.

Domain change or migration
URL restructuring
Permanent content relocation
SEO value transfers to new URL

302 Found

Temporary Redirect

Use for temporary redirects where the original URL should still be used in the future.

Maintenance page redirect
A/B testing scenarios
Temporary content relocation
SEO value stays with original URL

What is the difference between 400 and 422?

400 Bad Request

Malformed Request

The request is malformed — the server cannot parse it.

Invalid JSON syntax
Malformed XML structure
Missing required headers
Syntax-level errors

422 Unprocessable Content

Semantic Error

The request is syntactically correct but semantically invalid.

Valid JSON but invalid field values
Business logic validation failures
Data type mismatches
Semantic-level errors

What does 502 Bad Gateway mean?

A 502 Bad Gateway error means that a server acting as a gateway or proxy received an invalid response from the upstream server.

Common Causes

Reverse proxy (like Nginx) cannot reach the backend application
Backend server is down or overloaded
Backend returns a malformed response
Network connectivity issues between proxy and backend
Timeout waiting for upstream server response

Troubleshooting Tip: Check your backend application logs and ensure the upstream server is running and accessible from the proxy server.

Are my pinned codes saved?

Yes. Pinned codes are saved in your browser's local storage and will persist across page refreshes and browser sessions.

No account or server connection needed
Data stored locally in your browser
Persists across sessions and page refreshes
Private to your browser only

Note: If you clear your browser's local storage or use a different browser/device, your pinned codes will not be available. Pins are device and browser-specific.