Mock HTML endpoint returning HTTP 400
https://demo-html-400.supercrontab.com/ answers every request with HTTP 400 Bad Request and a small HTML body. No signup, CORS enabled, nothing logged. Use it to see how your client, retry logic or cron job behaves on a 400 before it happens in production.
Live demo endpoint
Any method, any path. Returns 400 Bad Request with Content-Type: text/html; charset=utf-8. OPTIONS returns 204 with CORS headers.
Call it with curl
curl -i https://demo-html-400.supercrontab.com/
Call it with fetch
const res = await fetch("https://demo-html-400.supercrontab.com/");
console.log(res.status); // 400
const body = await res.text();What HTTP 400 Bad Request means
- When you see it
- The server could not understand the request: malformed JSON, a missing field or a wrong parameter type.
- What a client should do
- Fix the request before sending it again. Log the response body, it usually names the bad field.
- Retry?
- No
Sample response body
<!doctype html> <html> <head><title>Mock page</title></head> <body><h1>ok</h1><p>id 42</p></body> </html>
A tiny page. Useful for scrapers, uptime monitors and testing how a client treats HTML error pages.
Questions
Does this endpoint really return HTTP 400 every time?
Yes. Every GET, POST, PUT, PATCH or DELETE to https://demo-html-400.supercrontab.com/ gets status 400 Bad Request with a small HTML body, whatever the path, query or headers. OPTIONS gets 204 with CORS headers so browsers can preflight.
Should my client retry a 400?
No. Retrying the same request cannot change the outcome. Fix the request before sending it again. Log the response body, it usually names the bad field.
Can I get a different format, a delay or a custom body?
The same status is available in JSON, XML, Text, CSV, YAML, RSS, JavaScript. 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.