📖 HTTP Status Code Dictionary

Explanation in Japanese of the meaning, usage, and application of all HTTP status codes. Search, filter, and bookmark functions included.

🔍

Comparison of commonly confused codes

301 vs 302 -- Redirect Differences

301 Moved Permanently

Permanent redirect. Used when URL has permanently changed. Search engines transfer SEO value to new URL. Recommended for domain migration or URL restructuring.

302 Found

Temporary redirect. Used when original URL may be used again. Used for temporary redirects during maintenance, A/B testing, etc.

401 vs 403 -- Authentication vs Authorization

401 Unauthorized

Authentication required. Returned when not logged in or token is invalid. Access may be granted with correct credentials.

403 Forbidden

Access forbidden. Returned when authenticated but lacking permissions. Used when regular users access admin-only pages.

500 vs 502 -- Server Error Differences

500 Internal Server Error

Internal server error. Caused by bugs, misconfigurations, or unhandled exceptions. Check server logs to identify the cause.

502 Bad Gateway

Gateway error. Occurs when reverse proxy (Nginx, etc.) receives invalid response from backend. Caused by backend downtime or timeout.

Usage and Application Examples

  • Reference for response code selection during API development
  • For checking when designing web site error pages
  • Correctly set redirect codes for SEO
  • Bookmark function for quick reference to frequently used codes

What is HTTP Status Code Dictionary?

The HTTP Status Code Dictionary is a comprehensive reference guide explaining all HTTP response codes (1xx through 5xx) used in web communication. Each code entry includes the technical meaning, real-world usage context, and common applications. Essential for developers, system administrators, and DevOps professionals troubleshooting server issues and understanding web protocol behavior.

How to Use

Browse the complete list of HTTP status codes organized by category: 1xx (Informational), 2xx (Success), 3xx (Redirection), 4xx (Client Error), and 5xx (Server Error). Click on any status code to view its detailed explanation, including what triggered it and how servers use it. Search functionality lets you find specific codes by number or keyword—search "redirect" to find all 3xx codes, or "unauthorized" to locate authentication-related errors. Each entry explains the code's role in client-server communication, when it occurs, and typical remediation steps. Use this as a reference while reviewing server logs, debugging API responses, or configuring web applications.

Use Cases

Web developers troubleshoot API integrations by looking up status codes in error responses; a 429 (Too Many Requests) indicates rate limiting, while 401 (Unauthorized) signals authentication failure. DevOps engineers monitoring server health use this dictionary to interpret log files and set up appropriate alerts—500 errors trigger incident response, while 302 redirects indicate normal routing. System administrators analyzing website traffic patterns reference this guide to understand user experience issues—404 (Not Found) errors reveal broken links needing correction. Frontend developers handle API errors gracefully by implementing code-specific responses—retry logic for 5xx errors, user prompts for 401/403. IT support staff explain status codes to non-technical stakeholders when websites malfunction. SEO professionals research 301 (Moved Permanently) versus 302 (Found) to properly redirect old URLs without losing ranking. Quality assurance testers verify correct status codes in API responses during application testing.

Tips & Insights

Remember the 2xx range indicates success (200 OK, 201 Created), while 4xx errors are client-side problems and 5xx errors are server-side issues—this distinction guides troubleshooting direction. Status code sequences matter: a 301 redirect followed by 200 is normal; a 301 loop indicates misconfiguration. Use cURL or browser developer tools (Network tab) to see actual status codes your application receives. For APIs, combine status codes with response bodies for complete error information. Implement exponential backoff when receiving 5xx or 429 responses. Understanding codes helps predict system behavior and build resilient applications. Keep a bookmark to this reference for quick lookup during development and troubleshooting.

Frequently Asked Questions

What is an HTTP status code?

The HTTP status code is a three-digit number returned by the web server in response to a client (browser) request. It indicates the result of processing the request (success, redirect, error, etc.).

What types of status code categories are available?

They fall into five categories: 1xx (information), 2xx (success), 3xx (redirect), 4xx (client error), and 5xx (server error).

What are the most commonly used HTTP status codes?

200 (success), 301 (permanent redirect), 302 (temporary redirect), 404 (page not found), and 500 (internal server error) are most commonly used.

What is the difference between 301 and 302 redirects?

301 is a permanent redirect, indicating that the URL has changed permanently; 302 is a temporary redirect, meaning that the original URL may be used again in the future. 301 is recommended for SEO purposes.

What is the difference between a 4xx error and a 5xx error?

4xx errors indicate client-side problems (incorrect URLs, authentication errors, etc.) and 5xx errors indicate server-side problems (internal errors, overload, etc.). 4xx errors can be corrected by the user and 5xx errors must be addressed by the server administrator.

Is the data in this tool secure?

Yes, the tool does not require any external data to be sent. This tool works entirely within your browser and does not send any data externally. Bookmark information is stored in your browser's LocalStorage.

What is HTTP status code 302?

HTTP 302 Found is a status code indicating a temporary redirect. It means the requested resource has temporarily moved to a different URL, and future requests should still target the original URL. In SEO, it is distinguished from 301 (permanent redirect).

What is HTTP status code 499?

499 Client Closed Request is a Nginx-specific status code not included in the official HTTP specification. It is recorded when a client closes the connection before the server sends a response. It occurs when a connection times out or when a user closes their browser while a page is loading.

What does HTTP status code 200 mean?

A 200 status code indicates a successful request has been fulfilled. The server processed your request correctly and returned the requested resource or data without any errors, making it the most common status code in successful web interactions.

How do I fix a 404 Not Found error?

A 404 means the requested page or resource doesn't exist on the server. First, check the URL for typos or incorrect capitalization, verify the file path is correct, or contact the website administrator to see if the resource was moved, deleted, or renamed.

What's the difference between 503 Service Unavailable and other 5xx errors?

A 503 specifically means the server is temporarily unavailable, usually due to maintenance or overload, and should resolve when the server recovers. Other 5xx errors indicate persistent server problems like 500 (Internal Server Error) or 502 (Bad Gateway) that may require longer to fix.

When should a server use 301 vs 302 vs 307 redirects?

Use 301 for permanent moves (tells search engines to update their index), 302 for temporary redirects, and 307 when the HTTP method should remain unchanged. Search engines and browsers treat these differently, so choosing the right code ensures proper caching behavior and SEO handling.

What does the 1xx status code category mean?

1xx codes are informational responses indicating the request was received and processing is continuing. Examples include 100 Continue (server is ready for request body) and 101 Switching Protocols; these are rarely seen in modern web usage since the connection usually completes before returning these codes.

How do caching and status codes relate?

Status codes like 304 Not Modified tell browsers to use cached versions instead of downloading new data, while 200 OK responses may include caching headers. Understanding this relationship helps optimize website performance and reduce server load by leveraging client-side caching effectively.