503 Service Unavailable

What This Error Means

The server is currently unable to handle the request due to temporary overloading or maintenance.

Server temporarily unavailable.

Common Causes

• Server maintenance
• Server overloaded
• Too many connections
• Resource exhaustion
• Application restart

How to Fix It (For Visitors)

• Wait a few minutes and try again
• Check Retry-After header
• Visit status page

How to Fix It (For Developers/Admins)

• Check server resources (CPU, RAM, disk)
• Scale infrastructure
• Implement load balancing
• Set Retry-After header
• Check database connections
• Review application pool settings

Code Examples

Here's how to return a 503 status code in various programming languages:

Python (Flask)

from flask import Flask, jsonify

app = Flask(__name__)

@app.route('/endpoint')
def endpoint():
    return jsonify({"message": "Service Unavailable"}), 503

Node.js (Express)

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

app.get('/endpoint', (req, res) => {
    res.status(503).json({ message: 'Service Unavailable' });
});

PHP

<?php
http_response_code(503);
header('Content-Type: application/json');
echo json_encode(['message' => 'Service Unavailable']);
?>

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(503)
    json.NewEncoder(w).Encode(map[string]string{
        "message": "Service Unavailable",
    })
}

Java (Spring Boot)

@GetMapping("/endpoint")
public ResponseEntity<Map<String, String>> endpoint() {
    Map<String, String> response = new HashMap<>();
    response.put("message", "Service Unavailable");
    return ResponseEntity.status(503).body(response);
}

Ruby (Sinatra)

get '/endpoint' do
    status 503
    json message: 'Service Unavailable'
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 6.6.4.

View on IANA HTTP Status Code Registry →