Interop 2027 proposals close on September 23, and untested ideas do not qualify
The call for Interop 2027 Focus Area proposals opened on September 3, 2026 and closes on September 23, 2026. Proposals are filed as issues on the web-platform-tests/interop repository, and two conditions decide almost everything: the technology must already have a mature standard, and it must be testable, because the test results are what the dashboard scores. Anything that fails the second condition is steered toward an Interop Investigation instead. Twenty days is the whole window, and the evidence a good proposal needs takes longer than an evening to assemble.
Every year the Interop project picks a short list of things browser engines will work on together, and every year that list starts as issues written by ordinary web developers. The 2027 window opened on September 3, 2026 and closes on September 23, 2026, which is twenty days from a WebKit blog post signed by Yulun Wu.
Two conditions decide most of it
A Focus Area proposal needs a mature standard behind it, from the W3C, TC39, or another standards venue, and it needs to be testable. Those two are connected: a written standard is what makes automated Web Platform Tests possible, and the test results are what the Interop dashboard scores. An idea for a technology that ought to exist but does not yet have a specification belongs in the standards venue itself, not in this repository.
If the technology exists and is specified but has thin test coverage, there is a second track. Interop Investigations are assignments the project gives itself to improve the state of testing, and that is where a proposal without enough tests should go.
- One feature, or a narrow group of related features, per proposal —
font-size-adjustrather than typography. - Name the interoperability problem concretely, and use cases from your own work carry more weight than general claims.
- Link the stable standard, then link the existing WPT coverage, and say how missing tests could be written this autumn.
- If someone already filed the same idea, add to that issue rather than opening a second one.
What a proposal has to argue
The post asks proposers not to assume the reader followed last year's discussion or knows how developers use every corner of the platform. The case has to be made inside the proposal itself: why this problem and not the hundreds of others, how the current situation slows people down, how many sites are affected, and what evidence there is that other people feel the same pain.
That is a bar that rewards preparation over enthusiasm. Survey data, a list of workarounds a team currently maintains, a bug that has been filed against three engines separately — this is the material that separates a proposal from a wish.
Why twenty days is the real constraint
The deadline is short relative to what the criteria ask for. Finding the stable specification is quick; assembling test coverage numbers and honest evidence of demand is not. One reasonable reading of the schedule is that it favors people who already have the receipts from their own work, which is exactly the group the project wants to hear from.
For a developer, this is one of the few moments in the year when the effort-to-influence ratio on the web platform is genuinely good. An issue that takes an afternoon to write can put a bug you have worked around for two years on next year's shared agenda.
„There are two essential criteria that all successful Focus Area proposals will have.“
Related
Safari 27.0 ships an MCP server, so a coding agent can drive the browser itself
WebKit published the feature list on September 17, 2026, and it is the longest the team has written: 83 features, up from 58 at the first beta in June, and 844 quality fixes against the 525 announced at WWDC. The headline for anyone who builds with a coding agent is the Safari MCP server, which hands the agent the DOM, network requests, screenshots and console output from a real Safari window. Customizable Select turns the real select element into something you can fully restyle, and scroll anchoring stops the page from jumping when content loads in above what you are reading.
WebKit Blogverified
Safari Technology Preview 252 adds named-feature() and lets SVG reach a filter in another file
The preview build came out on September 11, 2026 and covers WebKit changes between 319252@main and 320112@main. Eleven features are new, and two of them extend the same job: how a stylesheet, and then a script, finds out what the engine underneath can do. The named-feature() function asks about a behavior that has no syntax of its own, and the registry behind it holds exactly two entries today. SVG also gained external resources, so the url() reference can finally point at a filter, mask or gradient stored in another document.
WebKitverified
Safari 27 fixes top-level await, after WebKit rewrote the module loader in C++
WebKit published the fix on September 2, 2026. Dynamic imports of a module that uses top-level await could complete out of order in Safari, and an importer that ran early hit an error about accessing a value before initialization. The cause was a module loader built on the abandoned WHATWG Loader proposal rather than on the algorithms in the ECMAScript standard. WebKit rewrote the loader from self-hosted JavaScript into native C++, and the result ships in Safari 27 and in Safari Technology Preview 251.
WebKitverified