HTTP headers / request header

If-Match

If-Match: "33a64df551425fcc"

What it does

Conditional write: "apply my PUT/PATCH/DELETE only if the resource still has this ETag". The backbone of optimistic locking; mismatch → 412.

The gotcha

APIs answering 428 are demanding exactly this header — fetch, take the ETag, retry.

Debugging headers on a phone

The fastest way to see what If-Match is actually doing is to send the request and read both sides raw — ReqPad shows auto-generated and custom headers for every request, on all six protocols, with history. Related references: status codes · Authorization · Accept · Accept-Encoding · Accept-Language · If-None-Match · If-Modified-Since

Inspect If-Match on a live request.

Build the request, send it, read raw headers and timing — from your iPhone. Free to start.

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