Web developers have spent years working around the differences between browsers, but the industry’s annual Interop project is designed to chip away at those compatibility problems one feature at a time. Now, the teams behind major browsers are asking developers to help decide what should be tackled next.

Microsoft has opened the proposal process for Interop 2027, giving developers, framework authors, standards contributors, and other members of the web community until September 23, 2026, to suggest web platform areas that need better interoperability. The final Interop 2027 scope is expected to be published in early February 2027.

Interop is a collaborative effort involving browser vendors and the broader web platform community. Its goal is straightforward: make standards-based web technologies behave more consistently across browsers so developers don’t have to build around browser-specific quirks.

The project has already focused on technologies including CSS layout and utilities, View Transitions, CSS Anchor Positioning, popovers, and Shadow DOM. Microsoft says browser vendors are also continuing work across areas such as the Navigation API, WebRTC, WebTransport, dialogs and popovers, custom highlights, and container style queries.

Developers can help choose what comes next

The Interop 2027 proposal process is aimed at problems developers are actually encountering today. Microsoft is specifically asking for submissions involving web platform features that behave differently between browsers, standards-based capabilities that remain difficult to depend on, or areas where improved interoperability could unlock new possibilities.

That makes the process more than a browser vendor roadmap. Interop proposals are intended to reflect the practical problems developers face when building and maintaining websites and web applications.

A strong proposal should demonstrate a real-world developer problem and explain how inconsistent browser behavior or incomplete support creates friction. Evidence from frameworks, libraries, issue trackers, surveys, or real-world websites can also help demonstrate that the problem has meaningful ecosystem impact.

The proposals also need to be based on established web standards. Interop isn’t intended to decide which new technologies should be invented; instead, it focuses on existing standards where browser implementations can become more consistent.

WebKit’s own call for Interop 2027 proposals makes a similar distinction. The project favors technologies with mature standards and enough testing infrastructure to measure interoperability. New ideas that don’t yet have a stable standard are better suited to the relevant standards organizations, while technologies lacking sufficient testing may instead be candidates for Interop investigations.

Testing is a key part of Interop

One of the most important requirements for an Interop proposal is that progress must be measurable.

The project relies on Web Platform Tests, or WPT, to evaluate how consistently browsers implement a particular technology. Microsoft says proposals should therefore have strong existing test coverage or a clear path toward creating the tests needed to measure progress.

That also means narrowly defined proposals are generally more useful than broad requests. Asking browsers to simply “improve CSS,” for example, doesn’t provide a sufficiently clear target. A focused feature or specific interoperability problem gives the Interop team something concrete to evaluate and measure.

WebKit similarly recommends that proposals identify a specific interoperability issue, explain its impact, point to the relevant stable standard, and provide information about existing WPT coverage.

This approach has helped Interop turn browser compatibility from a vague industry problem into something that can be tracked with concrete scores and tests.

Interop has already tackled major web technologies

The importance of the project is easier to see through the technologies it has previously targeted.

Features such as View Transitions, CSS Anchor Positioning, popovers, and Shadow DOM have benefited from the focused interoperability work. Microsoft says browser vendors have continued collaborating on a wide range of web platform features during the current Interop cycle as well.

Igalia, another participant in the project, points to the measurable improvements Interop has produced in previous years. The company notes that Interop 2025 focus areas saw scores ranging from 29% to 97%, while the 2026 areas were ranging from 39% to 89% as of late August.

The numbers illustrate the project’s basic premise: browser interoperability can be treated as an engineering problem that can be measured and improved rather than simply accepted as an unavoidable part of web development.

The deadline is September 23

Developers interested in influencing Interop 2027 have until September 23, 2026, to submit their proposals. The Interop team will then evaluate the submissions through its selection process before publishing the final scope in early February 2027.

Microsoft is encouraging developers to submit ideas even when they’re uncertain whether a proposal will ultimately qualify. Unselected proposals can still provide useful signals about where developers are experiencing compatibility problems, and Microsoft says those requests can feed into its broader Top Developer Needs tracking.

The proposal process is also collaborative. Developers can support existing proposals and contribute evidence rather than submitting duplicate requests, giving the broader web community a chance to make the case for the issues that matter most.

For web developers, that may be the most important part of Interop 2027. Browser compatibility is ultimately experienced at the code level, and the people building websites every day are often the ones best positioned to identify which inconsistencies cause the most trouble.

If Interop continues to focus on those high-impact problems, the result should be a web where developers spend less time asking why something works in one browser but not another—and more time building the experience itself.