The Interop Project is a cross-browser initiative to improve web compatibility in areas that offer the most benefit to both users and developers.
The group, including Apple, Google, Igalia, Microsoft, and Mozilla, takes proposals of features that are well defined in a sufficiently stable web standard, and have good test suite coverage. Then, we come up with a subset of those proposals that balances web developer priorities (via surveys and bug reports) with our collective resources.
We focus on features that are well-represented in Web Platform Tests as the pass-rate is how we measure progress, which you can track on the Interop dashboard.
Once we have an agreed set of focus areas, we use those tests to track progress in each browser throughout the year. And after that, we do it all again!
But, before we talk about 2026, let’s take a look back at Interop 2025…
Interop 2025
Firefox started Interop 2025 with a score of 46, so we’re really proud to finish the cycle on 99. But the number that really matters is the overall Interop score, which is a combined score for all four browsers – and the higher this number is, the fewer developer hours are lost to frustrating browser differences.
The overall Interop score started at 25, and it’s now 95. As a result, huge web platform features became available cross-browser, such as Same-Document View Transitions, CSS Anchor Positioning, the Navigation API, CSS @scope, and the URLPattern API.
That’s the headline-grabbing part, but in my experience, it’s way more frustrating when a feature is claimed to be supported, but doesn’t work as expected. That’s why Interop 2025 also focused on improving the reliability of existing features like WebRTC, CSS Flexbox, CSS Grid, Pointer Events, CSS backdrop-filter, and more.
But it’s not just about passing tests
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