For browsers →
Does an image of a green check mark appear?
For other clients
Make a request to https://early-hints.fastlylabs.com/test.png; if your client can correctly load that file, it passes.
This page tests browsers and other HTTP clients for compatibility with the 103 Early Hints status code.
Passing means that the client doesn't break when receiving a non-final status code like 103; it doesn't mean that they'll actually do anything with the hints.
Does an image of a green check mark appear?
Make a request to https://early-hints.fastlylabs.com/test.png; if your client can correctly load that file, it passes.
Did this test identify a problem with your client? If so, please fill out an error report.