Deprecation reports

Some browser features, functions, or APIs are considered deprecated, no longer recommended, and while they still work, you shouldn't be using them. Deprecation reporting will send you a report if your code uses such deprecated feature, all you need to send is a Report-To response header.

The Report-To response header:

Report-To: {"group":"default","max_age":1800,"endpoints":[{"url":""}],"include_subdomains":true}

Use a deprecated feature

Synchronous XMLHttpRequest outside of workers is in the process of being removed as it has detrimental effects to the user's experience and browsers have deprecated such usage. Developers must not pass false for the async argument of the open() method but you're a professional driver and this is a closed circuit, so…

by calling new XMLHttpRequest().open('GET', 'foo', false)

show the code

Use an invalid feature

Some features are considered invalid, and won't work at all, for example using <source src> HTML element with a <picture> parent, instead of <source srcset>. But you will still get a report if you use them.

instead of <source srcset>

show the code

See Chrome's source code for more deprecated and invalid features.

Related specs & documents