501 Not Implemented

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HTTP

501 Not Implemented

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

What it means

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

Likely cause

An HTTP method or feature the server does not recognize or has not implemented, or a missing handler behind a proxy.

How to fix it

Use a standard, supported request method. Site owners: implement the required method/feature or fix the proxy/gateway that is passing an unknown request upstream.

Other HTTP errors

400 Bad Request The server could not understand the request. 401 Unauthorized Authentication is required and has failed or was not provided. 403 Forbidden The server understood the request but refuses to authorize it. 404 Not Found The requested page or resource does not exist on the server. 405 Method Not Allowed The server recognizes the request method but the target resource does not allow it. 408 Request Timeout The server timed out waiting for the client to finish sending the request. 409 Conflict The request conflicts with the current state of the target resource. 410 Gone The requested resource is permanently gone and no forwarding address is available. 413 Payload Too Large The request body is larger than the server is willing or able to process. 415 Unsupported Media Type The server refuses the request because the payload's media type is unsupported. 422 Unprocessable Content The server understood the request and its syntax but cannot process the contained instructions. 429 Too Many Requests The client has sent too many requests in a given amount of time and is being rate-limited. 431 Request Header Fields Too Large The server refuses the request because its header fields are too large, individually or collectively. 451 Unavailable For Legal Reasons The resource is unavailable because of a legal demand to block access to it. 500 Internal Server Error A generic server-side failure while processing the request. 502 Bad Gateway A gateway or proxy received an invalid response from the upstream server. 503 Service Unavailable The server is temporarily unable to handle the request. 504 Gateway Timeout A gateway did not receive a timely response from the upstream server. 301 Moved Permanently The resource has permanently moved to a new URL and clients should use the new location from now on. 302 Found The resource is temporarily available at a different URL while the original URL remains canonical. 304 Not Modified The resource has not changed since the client's cached copy, so no body is returned. 307 Temporary Redirect The resource is temporarily at a different URL and the request method and body must be preserved on redirect. 308 Permanent Redirect The resource has permanently moved and the request method and body must be preserved on redirect.

About Error Code Lookup

The Error Code Lookup is a searchable directory of more than 200 common error messages and codes across 12 categories: HTTP status codes, Windows error codes, browser and network errors, JavaScript, Python, PHP, Node.js and npm, Java, MySQL, Git, Linux shell errors and email/SMTP codes. Every entry is written in plain language for quick troubleshooting.

Each error is explained in three parts: what the message actually means, what usually causes it and concrete steps to fix it. That structure turns a cryptic string like ERR_CONNECTION_REFUSED or 0x80070005 into an actionable checklist instead of a guessing game.

You can filter the list by category, search by code, constant or message fragment, and copy any code with one click. Every error also has its own dedicated page with related errors from the same category, so you can bookmark or share a direct link to the exact fix.

How to use Error Code Lookup

  1. Type the error code or message into the search box — for example 404, ERR_NAME_NOT_RESOLVED or 0x80070005.
  2. Narrow the results with the category filter (HTTP, Windows, JavaScript, MySQL and so on) if the search returns too many entries.
  3. Open the matching entry to read what it means, its likely cause and how to fix it.
  4. Use the copy button to grab the exact code for a bug report or support ticket.
  5. Check the related errors section for other errors from the same category.

Frequently asked questions

It covers 12 categories: HTTP status codes, Windows system errors, browser and network errors, JavaScript, Python, PHP, Node.js and npm, Java, MySQL, Git, Linux shell errors and email/SMTP reply codes — more than 200 entries in total.

Search with fewer words. The shortest unique part works best: just the numeric code (“404”, “0x80070005”) or the constant name (“ERR_NAME_NOT_RESOLVED”) rather than the full sentence your system printed.

Yes. Each entry has a dedicated detail page explaining the meaning, likely cause and fix, plus related errors from the same category. You can bookmark it or send the link directly to a colleague or a support ticket.

The fixes describe the standard, widely accepted resolution for each error. Still, read the likely-cause section first — the same code can have several triggers, and matching the cause to your situation tells you which fix applies.

Yes, it is completely free. You can search, browse the category directory and open as many error detail pages as you need without an account.
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