Content type in Resource Timing

Category: Performance
Type: New or changed feature
Status: In development (Chrome In development)
Intent stage: Evaluate readiness to ship

Summary

Adds the contentType field to PerformanceResourceTiming to hold a string corresponding to the content type of the fetched resource as returned by the server.

Motivation

Servers and CDNs sometimes "swap out" file formats transparently (URL doesn't change) based on User Agent string or Client Hints when responding to a request for a resource. By providing access to the content type in those cases it would be possible to knowing exactly which format has been used

Standards & signals

Specification: https://github.com/w3c/resource-timing/pull/341
Firefox: Shipped/Shipping — Shiped in Firefox 129 (August 2024)
Safari: Support — Bug: https://bugs.webkit.org/show_bug.cgi?id=247887
Web developers: Positive
Tracking bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1366706

Samples: https://github.com/abinpaul1/resource-timing/blob/explainer-content-type/Explainers/Content-Type.md#api-changes-and-example-code

Explainers: https://github.com/abinpaul1/resource-timing/blob/explainer-content-type/Explainers/Content-Type.md

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