505 HTTP Version Not Supported

What This Error Means

The server does not support the HTTP protocol version used in the request.

Server doesn't support the HTTP version in the request.

Common Causes

• Client using HTTP/2 with HTTP/1.1-only server
• Outdated server software
• HTTP version mismatch

How to Fix It (For Visitors)

• Update your browser
• Contact website administrator

How to Fix It (For Developers/Admins)

• Update server software
• Enable HTTP/2 support
• Configure protocol versions
• Update Nginx/Apache

Code Examples

Here's how to return a 505 status code in various programming languages:

Python (Flask)

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/endpoint')
def endpoint():
    return jsonify({"message": "HTTP Version Not Supported"}), 505

Node.js (Express)

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

app.get('/endpoint', (req, res) => {
    res.status(505).json({ message: 'HTTP Version Not Supported' });
});

PHP

<?php
http_response_code(505);
header('Content-Type: application/json');
echo json_encode(['message' => 'HTTP Version Not Supported']);
?>

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(505)
    json.NewEncoder(w).Encode(map[string]string{
        "message": "HTTP Version Not Supported",
    })
}

Java (Spring Boot)

@GetMapping("/endpoint")
public ResponseEntity<Map<String, String>> endpoint() {
    Map<String, String> response = new HashMap<>();
    response.put("message", "HTTP Version Not Supported");
    return ResponseEntity.status(505).body(response);
}

Ruby (Sinatra)

get '/endpoint' do
    status 505
    json message: 'HTTP Version Not Supported'
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 6.6.6.

View on IANA HTTP Status Code Registry →