The HyperText Transfer Protocol (HTTP)
412 Precondition Failed client error response code indicates that access to the target resource has been denied. This happens with conditional requests on methods other than
HEAD when the condition defined by the
If-None-Match headers is not fulfilled. In that case, the request, usually an upload or a modification of a resource, cannot be made and this error response is sent back.
412 Precondition Failed
ETag: "33a64df551425fcc55e4d42a148795d9f25f89d4" ETag: W/"0815"
Avoiding mid-air collisions
With the help of the
ETag and the
If-Match headers, you can detect mid-air edit collisions.
For example, when editing MDN, the current wiki content is hashed and put into an
Etag in the response:
If the hashes don't match, it means that the document has been edited in-between and a
Precondition Failed error is thrown.
|RFC 7232, section 4.2: 412 Precondition Failed||Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests|
The information below has been pulled from MDN's GitHub (https://github.com/mdn/browser-compat-data).
The compatibility table in this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
|Chrome Full support Yes||Edge Full support 12||Firefox Full support Yes||IE Full support Yes||Opera Full support Yes||Safari Full support Yes||WebView Android Full support Yes||Chrome Android Full support Yes||Firefox Android Full support Yes||Opera Android Full support Yes||Safari iOS Full support Yes||Samsung Internet Android Full support Yes|
- Full support
- Full support