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428 Precondition Required

4xx client error

The server requires the request to be conditional, such as with If-Match, to prevent lost updates.

428 (RFC 6585) forces clients into safe concurrent editing. The server refuses unconditional writes: you must send If-Match with the ETag you last saw, so your update can't silently overwrite someone else's.

Class4xx Client Error
Retry?No — change the request first
Cacheable by defaultNo — only with explicit Cache-Control
Response bodyAllowed
Defined inRFC 6585 §3 — 428 Precondition Required
Example response
HTTP/1.1 428 Precondition Required
Content-Type: application/json
Content-Length: 33

{"error":"Precondition Required"}

Common causes

  • A PUT, PATCH or DELETE without If-Match, sent to an API that enforces optimistic concurrency.

How to fix it

  1. GET the resource, read its ETag, and send it as If-Match on the write.
  2. Be ready to handle 412 if the resource changed in between.

Send a 428 from your server

Express
res.status(428).json({ error: "Precondition Required" });
Next.js route handler
return Response.json({ error: "Precondition Required" }, { status: 428 });
Flask
return {"error": "Precondition Required"}, 428
Go net/http
http.Error(w, "Precondition Required", http.StatusPreconditionRequired)
nginx
return 428;

Check what a URL returns

Print just the status line from the command line, or check a whole list of URLs at once, with their response headers, in the HTTP Status Checker.

curl -sI https://example.com/your-path | head -n 1

Frequently asked questions

428 vs 412?

428: you didn't send a precondition and the server requires one. 412: you sent one and it failed.

Headers used with 428
Related status codes