The 501 error code means Not Implemented. The server received your request and understood that you asked for something, but it does not have the ability to do it. Most often the request used a method that the server software does not know at all.
This is a server side status in the 5xx family, so the visitor did nothing wrong. It also differs from a 405 Method Not Allowed. A 405 says this address cannot take that method, while a 501 says the server cannot do that method anywhere. You can see it as "501 Not Implemented", "HTTP error 501" or inside an installer or app as "error code 501".
Common causes
1Server software lacks the requested method
How to tellA special request type fails on every page of the site
What fixes itOwner updates the server software or adds the missing module
2Feature not built yet on the server
How to tellAn app or API call returns 501 with a message like not supported
What fixes itDeveloper builds the feature or removes the call from the app
3Proxy or gateway cannot pass the request on
How to tellDirect access works, but through the company proxy it fails
What fixes itAdmin adjusts the proxy or gateway rules
4Client sends a wrong or unusual request
How to tellA script or custom tool built the request by hand
What fixes itUse a standard method such as GET or POST and retest
5Outdated server or hosting stack
How to tellOld shared hosting that has never been upgraded
What fixes itMove to a current hosting setup or ask the host to upgrade
6Installer or app server returns 501
How to tellA download or install step in a desktop program stops with error 501
What fixes itCheck your connection, retry later, and contact the software's support
How to fix it, step by step
Reload once to rule out a glitch
Use F5 or the reload button. A 501 almost never fixes itself, but one reload costs nothing and confirms the error is steady.
Try the page from the home page
Open the site's main page and reach the same function by clicking through. A broken shortcut link sometimes carries an odd request type that the normal route avoids.
Test on another device or network
Open the same thing on another phone or on mobile data. If it fails everywhere, the server is the limit. If it works elsewhere, a proxy, work network or school filter on your side is interfering.
Update the app or restart the installer
If you see error code 501 inside an app or installer on Windows or Mac, update the app to its newest version from its official source, restart the computer and run the step again.
Turn off extensions that rewrite requests
Browser extensions that change headers or requests can create odd calls. Test in a private window with extensions off. If it works, turn them back on one by one until the problem returns.
Write to the site or app support
Tell them the page, what you pressed, the time and a screenshot of the error. Since a 501 means a missing server feature, only they can add it or change the request.
What the 501 error code means for the server
Web servers are built to understand a fixed set of request methods. When one arrives that the software does not recognise or has not been set up to carry out, the correct answer is 501. The standard also says a server that does not know a method should reply with 501. By comparison, a 405 is for a method the server knows but forbids on one address.
A file sharing tool tries to send a rarely used request type to your office server and gets 501 Not Implemented back. The server is running fine for normal browsing, but it simply has no code for that function.
501 versus 500, 502 and 405
| Code | Short meaning | Likely owner of the fix |
|---|---|---|
| 405 | Method known but not allowed here | Site owner |
| 500 | A failure inside the server software | Site owner |
| 501 | Server has no support for the request | Developer or host |
| 502 | Bad reply from a server behind a gateway | Site owner or host |
Read more on 500 Internal Server Error and 502 Bad Gateway, or open the HTTP status codes list.
How a REST API uses the 501 error code
Here, a 501 tells the caller that the server has not implemented the operation. It is common in early versions of a service where some endpoints exist as placeholders. Read the response body, which often names the missing feature, check the API documentation for supported operations and use a different one in the meantime. If you build the API, return 501 only for real missing support, and use 405 or 404 for everything else.
Error code 501 on a Mac or a Windows program
Some desktop programs print their own numbered messages, and one of them may say error code 501 during a download, sign in or update. These are not always the web status code. First check the internet connection and the date and time on the device, then update the program from its official page or store and try again. If the message stays, the program maker's support team can say what that number means in their product.
Do not install files from unknown sites that promise to remove such an error. They often carry malware.
Frequently asked questions
What is the 501 error code?
It is the HTTP status Not Implemented. The server does not support the feature needed to fulfil your request, so it refuses with a 501.
Can I fix a 501 error myself?
Seldom. You can reload, test on another network and update your app, but the real cure is for the owner or developer to add the feature or change the request.
What does error code 501 mean on an installer or app?
It depends on the program, since many apps use their own numbers. It often points to a failed request to the program's server. Check your connection, update the app and contact its support if it persists.
What is the difference between 501 and 405?
A 405 means that address does not allow that method. A 501 means the server does not support that method at all.
Is the 501 error code in a REST API a bug?
Not always. It can be a deliberate reply for a feature that is planned but not ready. If a feature should exist, report it to the API owner.