How do I fix a 428 Precondition Required?
Fetch the resource first, take its ETag, and send it in an If-Match header on your update. That proves you are editing the version you last saw.
HTTP 428 PRECONDITION REQUIRED
The server requires a conditional request, to prevent lost updates. 428 belongs to the 4xx client error class and is defined in RFC 6585.
Loading the workbench.
About HTTP 428
What Does HTTP 428 Precondition Required Mean?
The server requires a conditional request, to prevent lost updates. The code is registered with IANA and defined in RFC 6585.
Client error: the request has a problem, so it cannot be fulfilled as sent. Every code from 400 to 499 shares that general meaning, so a client that does not recognise 428 must treat it like 400.
When Do You See a 428 Response?
428 Precondition Required, from RFC 6585, means the server insists that this request be conditional. It is used to prevent lost updates: an API requires If-Match on PUT, PATCH, or DELETE so that clients cannot blindly overwrite a resource they have not fetched recently. Services with concurrent editing, such as document stores and configuration APIs, use it to force optimistic locking.
How Do You Fix a 428?
Clients should GET the resource, read its ETag, and send it back in If-Match on the modifying request. If the resource changed meanwhile, the server will then answer 412 and the client can merge. Servers should explain in the body which conditional header is required, and should not cache 428 responses. Document the requirement so client developers know to fetch before updating.
What Does a 428 Response Look Like?
HTTP/1.1 428 Precondition Required
Content-Type: application/json
Cache-Control: no-store428 is not cacheable by default: a browser or CDN stores it only when Cache-Control or Expires explicitly allows it.
To inspect a real one without sending it anywhere:
- Copy the response headers from your browser Network tab, or from
curl -i. - Paste them into the Header decoder to see every header explained.
- Check caching in the Cache lane.
Which Status Codes Are Related to 428?
- 412 Precondition Failed: An If-Match or If-Unmodified-Since condition was false. Used for optimistic locking.
- 409 Conflict: The request conflicts with the current state, such as an edit conflict or a duplicate.
- 304 Not Modified: The cached copy is still valid, so no body is sent. Answer to If-None-Match or If-Modified-Since.
Browse every code on the HTTP status codes page.
What Other Lanes Are in the Reference Section?
- HTTP status codes: Every IANA-registered status code, with a page per code.
- MIME types: File extensions to Content-Type, searchable both ways, plus a Content-Type parser.
- HTTP methods: GET, POST, PUT, PATCH, DELETE and the rest: safe, idempotent, cacheable.
Elsewhere in 2http: Header decoder, Cookie decoder, Cache-Control decoder, CORS checker, User-agent parser, and all eleven lanes on the 2http home page. Part of the 2suite.io privacy-first ecosystem.
Frequently Asked Questions
What is the difference between 428 and 412?
428 means you sent no precondition when one is required. 412 means you sent one and it turned out to be false.
Is HTTP 428 an error?
Yes. 428 is a client error response: the problem is in the request, so repeating it unchanged will usually fail again.
Is a 428 response cacheable by default?
No. Caches store a 428 only when Cache-Control or Expires explicitly allows it.
How Can You Verify That Nothing Leaves This Browser?
You do not have to take our word that your headers stay here. Developer tools show every request a page makes, so you can watch this page work and confirm that nothing is sent. The check takes under a minute.
- Open your browser developer tools with
F12, orCmd+Option+Ion a Mac, and select the Network tab. - Reload the page and let it finish. You will see the page's own files, its web fonts, and one anonymous page-view request. Nothing has been typed yet, so none of them can contain your headers.
- Click the clear icon in the Network tab so that the log is empty.
- Paste real headers into any lane and read the result.
- Look at the Network tab again. It is still empty. For extra proof, turn on offline mode after the page loads and every lane keeps working.
Only two things can add a line to that log, and neither carries your headers. Submitting the feedback form sends the vote and comment you typed. Typing characters in a script the page has not displayed yet, such as Cyrillic or Greek, can make the browser fetch the matching font file, and that request names only the font.
2http never sends a request on your behalf: the request builder writes code for you to run, and the meta inspector reads source you paste instead of fetching a URL. The production site also sends a Content-Security-Policy header that tells your browser to refuse connections to anywhere except this site and the anonymous analytics endpoint.