A2UI - 2026 Pricing, Features, Reviews & Alternatives

A2UI (Agent to UI) is an open-source declarative UI protocol, licensed under Apache 2.0, that defines how AI agents generate and stream rich, interactive user interfaces to client applications across web, mobile, and desktop surfaces. Rather than transmitting executable HTML or JavaScript, agents emit structured JSON component descriptions that client-side renderers translate into native widgets, eliminating the security risks associated with iframe-based or arbitrary code execution approaches. The protocol is transport-agnostic, operating over SSE, WebSockets, A2A, and AG-UI, and supports renderer implementations for Angular, Flutter, Lit, React, and Markdown.

The protocol architecture separates UI structure from application state through a flat adjacency list component model, allowing progressive rendering as agent output streams incrementally to the client. An extensible component catalog system, defined via JSON Schema, supports both standard and application-specific design system components, with catalog negotiation between agent and client ensuring compatibility. Bidirectional event handling supports user interactions, and per-surface catalog assignment enables multi-surface deployments. A visual Composer editor allows teams to generate valid A2UI JSON without local installation, and a Python agent SDK with ADK extension is available for agent-side integration. The protocol is interoperable with major agent frameworks including ADK, LangGraph, CrewAI, Mastra, Strands, and CopilotKit.

A2UI targets developers and enterprise teams building agent-driven applications, multi-agent systems, and agentic platforms. Its LLM-friendly declarative structure, including a Markdown-formatted catalog instructions field for design guidelines, makes it straightforward for generative models such as those powered by Gemini via ADK to produce valid UI descriptions at design time or runtime. Use cases include data entry forms, approval dashboards, and workflow automation interfaces. The protocol is versioned (v0.9.1 current, v1.0 candidate) and developed with contributions from Google, CopilotKit, and the broader open-source community.