Exact: A New Cross-Platform UI Framework for AI Agents
Build native applications for web, macOS, iOS, and Linux using a unified declarative language.
1Introducing the Exact Framework
Exact is a new cross-platform runtime designed for building applications that run natively on web, macOS, iOS, and Linux. It allows developers to write an interface once using a declarative language called Contract. Data logic is handled separately through TypeScript or Rust, ensuring high performance across all supported host environments.
2AI-First Development Philosophy
The framework is built with the assumption that AI agents will perform much of the coding. Agents can autonomously create, run, observe, and test applications without human intervention. This capability is integrated into the workflow, allowing developers to prompt agents to build features and verify them across multiple platforms simultaneously.
3How Contract Compiles Interfaces
The Contract compiler transforms interface descriptions into a compact plan consisting of tables and bytecode. At build time, constant data is baked into this plan, ensuring the first frame of an application requires no additional processing. This approach minimizes startup latency and ensures consistent rendering behavior across diverse hardware and software targets.
4Native Execution Without Bridges
Exact avoids traditional webview or JavaScript bridge architectures in the UI layer. Instead, a Rust runner executes the plan, while a layout kernel computes boxes using CSS rules. Platforms draw using their native tools, such as AppKit for macOS or UIKit for iOS, ensuring a truly native look and feel throughout.
5Performance and Layout Engine
The framework utilizes a patched Taffy engine for CSS layout calculations within a columnar node arena. On the web, the browser handles layout natively, meaning the web build remains lightweight without carrying an extra engine. Text measurement is handled by CoreText on Apple devices and cosmic-text on Linux systems for precision.
6Development Loop and Speed
Speed is a primary design principle, with performance budgets tracked on every commit. Regression issues are treated as high-priority tasks. The development loop is highly optimized, allowing developers to see changes in about a tenth of a second on the web, while native builds reuse previous artifacts to save time.
7Platform-Specific Capabilities
Exact does not force a lowest common denominator approach. Where platforms offer unique features, such as MapKit on Apple or real HTML in SVG foreignObjects on the web, the framework provides access to these native modules. This ensures developers can leverage the full power of each host platform while maintaining shared logic.
8System Requirements and Setup
Running Exact requires Rust, Bun, and Xcode for Apple platforms. The setup process involves installing pinned toolchains and the Hermes engine for TypeScript support on native hosts. The framework uses a dedicated script to verify dependencies and manage offline builds, ensuring that the development environment remains consistent and reproducible across machines.
9Testing with AI Agents
Testing is integrated into the agent workflow, allowing for automated verification on web, macOS, and iOS simulators. An agent can execute a test suite, capture screenshots, and confirm that the UI renders correctly. This automated feedback loop helps catch layout regressions or functional errors before they reach the production stage.
10Feedback and Data Privacy
The framework includes an optional feedback mechanism for recording friction during development. When enabled, it logs project metadata, exit codes, and command durations to Expo. Developers maintain full control over this data, as the system defaults to asking for permission before sending any information, and it never transmits actual source code.
11Current Project Maturity
Exact is currently in a pre-1.0 state and undergoes daily changes. By design, there is no API stability, backwards compatibility, or migration guide available at this time. Developers should expect breaking changes and are encouraged to follow the repository documentation closely while the framework evolves toward a more stable release.
12Strategic Implications for Developers
By unifying UI definitions and data logic, Exact reduces the overhead of maintaining separate codebases for different platforms. The focus on AI-agent compatibility positions it as a forward-looking tool for rapid application development. Its ability to generate native performance without standard webview bottlenecks makes it a significant development for cross-platform engineering.
Original article: Hacker News: Front Page — Exact: A New Cross-Platform UI Framework for AI Agents