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freesail

v0.9.4

Published

CLI and core libraries for Freesail - an open-source A2UI SDK

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Links

Maintainers

shanmugamnpmshanmugamnpm

Keywords

a2uifreesailagent-driven uigenerative uiai agent

Readme

Freesail

Agent-driven UI SDK — Enables AI agents to create and drive user interfaces.

Overview

Freesail enables AI agents to stream UI to supported clients using the A2UI Protocol. Agents render interfaces remotely without generating raw HTML or framework-specific code. The UI is defined through a schema-first catalog, keeping the agent and the frontend in sync.

Architecture

Freesail operates on a three-node pattern:

  • Agent: The intelligence layer that decides what to show, using MCP tools exposed by the Gateway.
  • Gateway: A Node.js bridge that connects to the agent via MCP and streams A2UI messages to the frontend via Server-Sent Events (SSE).
  • Frontend: The presentation layer (React) that receives A2UI messages and renders dynamic UI statefully.

Packages

| Package | Description | |---------|-------------| | freesail | CLI and core libraries for running and configuring Freesail | | @freesail/core | A2UI protocol definitions, parser, and transport | | @freesail/gateway | Node.js MCP bridge server | | @freesail/react | React renderer (<FreesailProvider> and surface hooks) | | @freesail/agent-runtime | Runtime library for building Freesail agents | | @freesail/standard-catalog | Standard UI component catalog (Text, Button, Chart, etc.) | | @freesail/chat-catalog | Chat interface component catalog | | @freesail/logger | Structured logging for the Freesail ecosystem |

Community packages are in packages/@freesail-community/.

Key Concepts

Catalogs

A catalog is a JSON schema that defines the components and functions an agent can use on a surface. The agent can only reference components declared in the catalog registered for that surface, preventing drift between the agent and the UI.

Surfaces

A surface is a named UI container within a client session. The agent creates surfaces, populates them with components, and updates their data model independently. Multiple surfaces can be active simultaneously within the same session.

Sessions

A client session represents a conversation thread. Sessions are identified by a unique ID and track active surfaces, client capabilities, and connection state (connected or suspended).

A2UI Protocol

A2UI is the JSON protocol for bi-directional communication between the gateway and the frontend.

Gateway → Frontend (SSE)

| Message | Description | |---------|-------------| | createSurface | Initialise a UI surface and load a catalog | | updateComponents | Send or update the component tree for a surface | | updateDataModel | Push data updates to a surface | | deleteSurface | Remove a surface and its components | | getDataModel | Request the current data model from the frontend (Freesail specific extension)| | getComponentTree | Request the current component tree from the frontend (Freesail specific extension) |

Frontend → Gateway (HTTP POST)

| Message | Description | |---------|-------------| | action | Report a user interaction | | error | Report a validation or runtime error |

MCP Tools

The Gateway exposes the following MCP tools to the agent:

| Tool | Description | |------|-------------| | create_surface | Create a new surface for a session | | update_components | Send components to a surface | | update_data_model | Update a surface's data model | | delete_surface | Delete a surface | | get_data_model | Retrieve the current data model from the frontend | | get_component_tree | Retrieve the current component tree from the frontend | | get_pending_actions | Drain pending user actions for a session | | get_all_pending_actions | Drain pending actions across all claimed sessions | | list_sessions | List active sessions owned by the agent | | get_catalogs | Get catalog definitions for a session | | get_component_details | Get detailed schema for specific components | | get_function_details | Get detailed schema for specific functions | | claim_session | Claim a client session for exclusive use | | release_session | Release a claimed session |

Documentation

www.freesail.ai

Maintainers & Contributors

Freesail is an open-source project. For support contact Thendral AI.

License

MIT — see LICENSE