501 Not Implemented

What This Error Means

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

Server doesn't recognize the request method or can't fulfill it.

Common Causes

• HTTP method not implemented
• Feature not supported
• Unrecognized request method

How to Fix It (For Visitors)

• Contact website administrator
• Use different client/browser

How to Fix It (For Developers/Admins)

• Implement the requested method
• Return 405 if method not allowed
• Update server software
• Enable required modules

Code Examples

Here's how to return a 501 status code in various programming languages:

Python (Flask)

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/endpoint')
def endpoint():
    return jsonify({"message": "Not Implemented"}), 501

Node.js (Express)

const express = require('express');
const app = express();

app.get('/endpoint', (req, res) => {
    res.status(501).json({ message: 'Not Implemented' });
});

PHP

<?php
http_response_code(501);
header('Content-Type: application/json');
echo json_encode(['message' => 'Not Implemented']);
?>

Go

package main

import (
    "encoding/json"
    "net/http"
)

func handler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json")
    w.WriteHeader(501)
    json.NewEncoder(w).Encode(map[string]string{
        "message": "Not Implemented",
    })
}

Java (Spring Boot)

@GetMapping("/endpoint")
public ResponseEntity<Map<String, String>> endpoint() {
    Map<String, String> response = new HashMap<>();
    response.put("message", "Not Implemented");
    return ResponseEntity.status(501).body(response);
}

Ruby (Sinatra)

get '/endpoint' do
    status 501
    json message: 'Not Implemented'
end

Browser Compatibility

Browser	Support	Notes
Chrome	✓ Full Support	All versions
Firefox	✓ Full Support	All versions
Safari	✓ Full Support	All versions
Edge	✓ Full Support	All versions

Official Specification

This status code is defined in RFC 7231 Section 6.6.2.

View on IANA HTTP Status Code Registry →