HTTP 428 Precondition Required

What does HTTP 428 mean?

The server requires the request to be conditional. An API can insist on If-Match for updates to prevent the “lost update” problem — clients must prove they saw the latest version before changing it.

4xx Client error: The request has a problem the client can fix: wrong URL, missing credentials, bad data or too many requests.

How to fix 428 Precondition Required

• Send the latest ETag in If-Match.

428 and SEO

Not relevant for web pages.

Example response

HTTP/1.1 428 Precondition Required

How to return a 428 response

Node.js (Express)

res.status(428).json({ error: 'Precondition Required' });

PHP

http_response_code(428);

Python (Flask)

return {'error': 'Precondition Required'}, 428

Go (net/http)

w.WriteHeader(428)

nginx

return 428;

Related status codes

• 412 Precondition Failed — A condition in the request headers (If-Match, If-Unmodified-Since) was not met.
• 409 Conflict — The request conflicts with the current state of the resource.

Check which status code a URL returns with the HTTP header checker.