HTTP 503 Service Unavailable Status Code - Test & Mock API

Code Examples

Here are examples of how to test HTTP 503 responses in different programming languages:

Select options below to see how to use advanced features in your code:

Add Custom Delay (x-delay) - Test timeout scenarios (1-60000ms)

Add Custom Headers (x-response) - Add custom HTTP headers to response

Add Custom Payload (x-payload) - Control entire response body with JSON

Request:

curl https://free.mockerapi.com/503

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

fetch('https://free.mockerapi.com/503')
  .then(response => {
    console.log('Status:', response.status); // 503
    return response.json();
  })
  .then(data => {
    console.log('Response:', data);
  })
  .catch(error => {
    console.error('Error:', error);
  });

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

import requests

response = requests.get('https://free.mockerapi.com/503')

print(f'Status Code: {response.status_code}')  # 503
print(f'Response: {response.json()}')

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

require 'net/http'
require 'json'

uri = URI('https://free.mockerapi.com/503')
response = Net::HTTP.get_response(uri)

puts "Status Code: #{response.code}"  # 503
puts "Response: #{JSON.parse(response.body)}"

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

package main

import (
    "fmt"
    "io"
    "net/http"
)

func main() {
    resp, err := http.Get("https://free.mockerapi.com/503")
    if err != nil {
        panic(err)
    }
    defer resp.Body.Close()

    fmt.Printf("Status Code: %d\n", resp.StatusCode)  // 503

    body, err := io.ReadAll(resp.Body)
    if err != nil {
        panic(err)
    }

    fmt.Printf("Response: %s\n", body)
}

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

import java.net.http.*;
import java.net.URI;

public class HttpStatusTest {
    public static void main(String[] args) throws Exception {
        HttpClient client = HttpClient.newHttpClient();
        HttpRequest request = HttpRequest.newBuilder()
            .uri(URI.create("https://free.mockerapi.com/503"))
            .GET()
            .build();

        HttpResponse response = client.send(request,
            HttpResponse.BodyHandlers.ofString());

        System.out.println("Status Code: " + response.statusCode());  // 503
        System.out.println("Response: " + response.body());
    }
}

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

Request:

const https = require('https');

https.get('https://free.mockerapi.com/503', (res) => {
  console.log('Status Code:', res.statusCode);  // 503

  let data = '';

  res.on('data', (chunk) => {
    data += chunk;
  });

  res.on('end', () => {
    console.log('Response:', JSON.parse(data));
  });
}).on('error', (err) => {
  console.error('Error:', err.message);
});

Response Headers:

HTTP/1.1 503 Service Unavailable
Content-Type: application/json
Access-Control-Allow-Origin: *

Response Body:

{
  "success": false,
  "status": 503,
  "statusText": "Service Unavailable - The server is not ready to handle the request",
  "timestamp": "2025-10-08T10:30:45.123Z",
  "request": {
    "method": "GET",
    "url": "/503",
    "fullUrl": "https://free.mockerapi.com/503"
  }
}

What is HTTP 503 Service Unavailable?

HTTP 503 Service Unavailable is a generic server-side error response that indicates the server encountered an unexpected condition that prevented it from fulfilling the request. This is a catch-all error status code when the server cannot be more specific about the error condition or when no other error status code is suitable.

Unlike client-side 4xx errors, a 503 error indicates that the problem is on the server's end, not with the client's request. The server should include information about the error condition in the response body, though specifics are often limited for security reasons.

When Does This Happen?

A 503 Service Unavailable response is returned when the server encounters an unexpected error that prevents it from processing the request. Common scenarios include:

Unhandled exceptions or runtime errors in server code
Database connection failures or query errors
Server misconfiguration issues
Resource exhaustion (memory, disk space)
Third-party service failures that the server depends on
Bugs in the application code

Try It Live

Click the button below to make a live request and see the 503 Service Unavailable response

Common Use Cases

🔥 Error Handling Testing

Test how your application handles critical server errors and displays appropriate error messages to users.

🎯 Monitoring & Alerting

Verify that your monitoring systems correctly detect and alert on 503 errors in production.

🔄 Retry Logic Testing

Test exponential backoff and retry mechanisms when encountering server errors.

📊 Analytics Integration

Ensure server errors are properly tracked in analytics and error reporting tools.

Service Unavailable

Code Examples

What is HTTP 503 Service Unavailable?

When Does This Happen?

Try It Live

Common Use Cases

🔥 Error Handling Testing

🎯 Monitoring & Alerting

🔄 Retry Logic Testing

📊 Analytics Integration

🛡️ Graceful Degradation

📝 Documentation Examples

Related Server Error Status Codes