HTTP Status Code 412 = “Precondition Failed”

The server rejected the request because one or more conditions specified in the request headers were not met.

Common causes

412 usually occurs with conditional headers like:

• If-Match
• If-None-Match
• If-Unmodified-Since
• If-Modified-Since

These headers are commonly used for:

• caching,
• concurrency control,
• preventing overwrite conflicts. Example with ETag

Client request

http id=”q8m2we”
PUT /document/1 HTTP/1.1
If-Match: “abc123”

Server resource has changed

http id=”v5k7ra”
ETag: “xyz999”

Response

http id=”n3p1xd”
HTTP/1.1 412 Precondition Failed

The update is rejected because the file/version changed.

Common real-world scenarios

• Collaborative editing systems
• APIs with version control
• Browser caching
• Cloud storage uploads
• REST APIs using ETags Why it exists

412 prevents:

• accidental overwrites,
• stale updates,
• cache inconsistencies,
• race conditions. Fixes

For users

• Refresh the page/data
• Retry the action
• Re-upload the latest version

For developers

1. Refresh ETag/version before update

Get latest resource first:

http id=”u9w4kc”
GET /document/1

Then retry update using latest ETag.

2. Remove incorrect conditional headers

Example:

http id=”g7q2mv”
If-Match: old-etag

3. Node.js example

js id=”r4k8zn”
if (req.headers[‘if-match’] !== currentEtag) {
return res.status(412).send(‘Precondition Failed’);
}

4. Laravel example

php id=”t6p3xe”
return response(‘Precondition Failed’, 412);

Difference between 409 and 412

| Code | Meaning |
| — | – |
| 409 | General conflict |
| 412 | Conditional header failed |

Common headers involved

| Header | Purpose |
| | |
| ETag | Resource version identifier |
| If-Match | Update only if version matches |
| If-None-Match | Cache validation |
| If-Unmodified-Since | Prevent stale updates |

Related HTTP status codes

| Code | Meaning |
| — | |
| 304 | Not Modified |
| 409 | Conflict |
| 412 | Precondition Failed |
| 428 | Precondition Required |