Interop 2026: Driving Web Consistency Across Browsers for a Fifth Year

Introduction

Web developers and designers alike understand the frustration of a feature working perfectly in one browser but breaking in another. For five years, the Interop Project has been tackling this challenge head-on. Interop 2026 is here, continuing the mission to make web technologies operate uniformly across all major browsers. This year, the collaboration includes Apple, Google, Igalia, Microsoft, and Mozilla—the same core group that has driven progress since the project’s inception.

What Is the Interop Project?

The Interop Project brings together the engineers behind the world’s leading browser engines to collaboratively improve the same set of web features within a single year. The goal is simple: ensure every feature behaves exactly as defined by its official web standard. By measuring conformance through Web Platform Tests, the project identifies and resolves inconsistencies, making the web a more reliable foundation for developers to build upon.

Focus Areas for 2026

Interop 2026 is ambitious, with twenty focus areas—fifteen new and five carryovers from Interop 2025. Each area represents a technology where cross-browser alignment is critical. Below is the full list, followed by deeper dives into a few key items.

• Anchor Positioning (carryover)
• Advanced attr()
• Container Style Queries
• contrast-color()
• CSS Zoom
• Custom Highlights
• Dialog and Popover Additions
• Fetch Uploads and Ranges
• getAllRecords() for IndexedDB
• JSPI for Wasm
• Media Pseudo-classes
• Navigation API
• Scoped Custom Element Registries
• Scroll-driven Animations
• Scroll Snap
• shape()
• View Transitions
• Web Compat
• WebRTC
• WebTransport

Anchor Positioning

Anchor Positioning, a carryover from 2025, already saw significant progress. This year’s focus is on clarifying the specification, resolving test issues, and improving reliability. The feature allows developers to position elements relative to each other—for example, attaching a tooltip to a button—without manual offset calculations. Full interoperability will unlock more dynamic and accessible layouts.

Advanced attr()

The CSS attr() function pulls values directly from HTML attributes into your stylesheets. Advanced attr() extends this capability, enabling more complex conversions and fallbacks. This reduces the need for JavaScript when creating context-aware designs, making pages faster and easier to maintain.

New Features Led by Safari

Safari has already shipped several of the included technologies. In fact, Apple’s browser was the first to implement contrast-color(), Media Pseudo-classes, shape(), and Scoped Custom Element Registries. Safari also supports Anchor Positioning, Style Queries, Custom Highlights, Scroll Snap, View Transitions, and more. By including these in Interop 2026, the project ensures that remaining gaps across other browsers are closed.

Additional Focus Areas Driving 20% of the Score

Four specific areas account for 20% of the Interop 2026 score: Advanced attr(), the getAllRecords() method for IndexedDB, WebTransport, and the JavaScript Promise Integration API for Wasm. These are exciting features that solve real needs—from more powerful CSS to better network communication and efficient WebAssembly integration.

How Interoperability Is Measured

The project relies on Web Platform Tests (WPT), automated test suites that verify browser behavior against official web standards. Passing these tests indicates that a feature is implemented correctly and consistently. Interop 2026 includes tests for all twenty focus areas, with scores updated regularly to track progress.

Looking Ahead

The fifth anniversary of Interop reflects a sustained commitment to a more predictable web. For developers, this means less time debugging cross-browser quirks and more time building great experiences. As the year progresses, expect updates on each focus area and, ultimately, a web that works the same for everyone—no matter the browser.