Mock JavaScript endpoint returning HTTP 503

https://demo-js-503.supercrontab.com/ answers every request with HTTP 503 Service Unavailable and a small JavaScript body. No signup, CORS enabled, nothing logged. Use it to see how your client, retry logic or cron job behaves on a 503 before it happens in production.

Live demo endpoint

https://demo-js-503.supercrontab.com/

Any method, any path. Returns 503 Service Unavailable with Content-Type: application/javascript. OPTIONS returns 204 with CORS headers.

Call it with curl

curl -i https://demo-js-503.supercrontab.com/

Call it with fetch

const res = await fetch("https://demo-js-503.supercrontab.com/");
console.log(res.status); // 503
const body = await res.text();

What HTTP 503 Service Unavailable means

When you see it: The service is overloaded or down for maintenance. Servers may include Retry-After to say how long.
What a client should do: Retry with exponential backoff and honour Retry-After. Circuit breakers should open after repeated 503s.
Retry?: Yes, with backoff

Sample response body

console.log("ok")

A script body with the application/javascript type. Test script loaders, CDNs and MIME checks.

Questions

Does this endpoint really return HTTP 503 every time?

Yes. Every GET, POST, PUT, PATCH or DELETE to https://demo-js-503.supercrontab.com/ gets status 503 Service Unavailable with a small JavaScript body, whatever the path, query or headers. OPTIONS gets 204 with CORS headers so browsers can preflight.

Should my client retry a 503?

Yes, with exponential backoff and a cap on attempts. Retry with exponential backoff and honour Retry-After. Circuit breakers should open after repeated 503s.

Can I get a different format, a delay or a custom body?

The same status is available in JSON, XML, Text, CSV, HTML, YAML, RSS. Delays, custom headers, error rates, request logging and your own body need a personal endpoint: sign up and create one at /endpoints in a minute, free.