What is Interop 2026?
For web developers and designers, few challenges are as persistent as ensuring a website behaves identically across different browsers. Even when browsers implement the same web technology, subtle differences in their engines can lead to inconsistent experiences. The Interop project addresses this by bringing together the major browser vendors—Google, Igalia, Microsoft, and Mozilla—to collaboratively improve a shared set of features each year. Now in its fifth iteration, Interop 2026 continues this mission, aiming to make the web platform more reliable and predictable for everyone.
The project measures success using Web Platform Tests, automated checks that verify whether browsers conform to official web standards. By focusing on alignment with these specifications, Interop 2026 accelerates progress toward a truly interoperable web. Apple’s Safari team has already implemented many of the featured technologies, including being the first browser to ship contrast-color(), media pseudo-classes, shape(), and Scoped Custom Element Registries. Other areas like Anchor Positioning, Style Queries, Custom Highlights, Scroll Snap, and View Transitions are also supported in Safari, but this year’s initiative ensures these features are fully interoperable across all engines.
Focus Areas for 2026
Interop 2026 covers twenty focus areas, fifteen of which are entirely new. The remaining five are carryovers from Interop 2025 (now resolved further). The complete list includes:
- 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
Additionally, four specific areas—advanced attr(), getAllRecords() for IndexedDB, WebTransport, and the JavaScript Promise Integration API (JSPI) for Wasm—collectively account for 20% of the Interop 2026 score. These are exciting new capabilities that address real developer needs.
Anchor Positioning
Carried over from Interop 2025, Anchor Positioning allows developers to place elements relative to a designated anchor point. Last year saw significant progress, and the 2026 focus is on clarifying the specification, resolving test issues, and increasing the reliability of this powerful layout feature.
Advanced attr()
The CSS attr() function bridges HTML attributes and visual styles, enabling more dynamic and context-aware designs without extra JavaScript. Interop 2026 aims to extend its capabilities and ensure consistent behavior across browsers.
Container Style Queries
Building on container queries for size, style queries allow components to adjust based on computed style values of their containers. This enhances modular design and component reusability.
contrast-color()
A new function that selects a color with sufficient contrast against a given background, directly in CSS. This simplifies accessibility and design systems.
CSS Zoom
The zoom property, historically non-standard, is being standardized to provide a reliable way to scale elements without disrupting layout.
Custom Highlights
Enables developers to define custom text highlights (e.g., search terms or annotations) using the CSS Custom Highlight API, improving editorial and search experiences.
Dialog and Popover Additions
Enhancements to the <dialog> element and popover attribute, including improved form handling and more flexible invocation patterns.
Fetch Uploads and Ranges
Standardizing upload progress and range requests in the Fetch API, critical for media streaming and large file transfers.
getAllRecords() for IndexedDB
Adds a method to retrieve all records from an IndexedDB object store in a single call, simplifying data access and performance.
JSPI for Wasm
The JavaScript Promise Integration API allows WebAssembly modules to use JavaScript promises, enabling asynchronous operations directly in Wasm code.
Media Pseudo-classes
New pseudo-classes like :playing and :paused for media elements, giving developers precise control over media playback styling.
Navigation API
A modern replacement for the history API, offering better control over navigation events and single-page application routing.
Scoped Custom Element Registries
Allows custom elements to be scoped to specific DOM subtrees, preventing naming collisions in large applications.
Scroll-driven Animations
Animates elements based on scroll position, using CSS alone—no JavaScript needed. Perfect for storytelling and interactive interfaces.
Scroll Snap
Improvements to the CSS Scroll Snap module for smoother, more predictable snapping behavior in scrollable containers.
shape()
The shape() CSS function defines geometric shapes for clipping and masking, enabling complex visual layouts without external assets.
View Transitions
Enables smooth animations between page navigations or DOM state changes, enhancing user experience with minimal code.
Web Compat
A broad focus area addressing alignment of browser behaviors with web standards, ensuring legacy sites work as intended.
WebRTC
Interoperability improvements for real-time communication APIs, including more consistent handling of media streams and network connections.
WebTransport
A modern protocol for low-latency, bidirectional communication, promising faster and more reliable data exchange than WebSockets.
With these twenty focus areas, Interop 2026 represents a significant step toward a seamless web experience. Developers are encouraged to test their sites against Web Platform Tests and follow progress on the Interop 2026 GitHub repository.