smithery.ai

ag-ui-protocol

AG-UI (Agent-User Interaction) protocol reference for building AI agent frontends.

First seen Mar 22, 2026

Installation

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Summary

AG-UI (Agent-User Interaction) protocol reference for building AI agent frontends.
Use when implementing AG-UI events (RUN_STARTED, TEXT_MESSAGE_*, TOOL_CALL_*, STATE_*), building agents that communicate with frontends, implementing streaming responses, state management with snapshots/deltas, tool call lifecycles, or debugging AG-UI event flows.

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More details

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Skill metadata

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Allowed toolsRead, Grep, Glob, Edit, Bash

Package contents

Files included with this skill beyond the listing page.

skill md SKILL.md 3,513 B
docs SUMMARY.md 369 B

History

Mar 22, 2026 First seen on skills.sh
Sep 9, 2026 First recorded snapshot · 1 installs

SKILL.md

AG-UI Protocol

The Agent-User Interaction (AG-UI) Protocol is an open, lightweight, event-based protocol that standardizes how AI agents connect to user-facing applications.

When to Use This Skill

Use this skill when:

Implementing AG-UI protocol events in your code
Building agents that communicate with frontends via AG-UI
Understanding the event types and their structure
Implementing state management, tool calls, or message streaming
Debugging AG-UI event flows

Documentation

See the docs/2025-11-27/ directory for complete AG-UI protocol documentation:

introduction.md - Protocol overview and integrations
concepts/architecture.md - Core architecture and design
concepts/events.md - Event types and patterns
concepts/messages.md - Message structure and types
concepts/state.md - State management and synchronization
concepts/tools.md - Tool definitions and lifecycle
concepts/agents.md - Agent implementation
concepts/middleware.md - Middleware patterns
concepts/serialization.md - Event serialization and compaction
quickstart/introduction.md - Getting started guide
quickstart/server.md - Server implementation
quickstart/clients.md - Client implementation

Quick Reference

Event Types

enum EventType {
  // Lifecycle
  RUN_STARTED = "RUN_STARTED",
  RUN_FINISHED = "RUN_FINISHED",
  RUN_ERROR = "RUN_ERROR",
  STEP_STARTED = "STEP_STARTED",
  STEP_FINISHED = "STEP_FINISHED",

  // Text Messages
  TEXT_MESSAGE_START = "TEXT_MESSAGE_START",
  TEXT_MESSAGE_CONTENT = "TEXT_MESSAGE_CONTENT",
  TEXT_MESSAGE_END = "TEXT_MESSAGE_END",

  // Tool Calls
  TOOL_CALL_START = "TOOL_CALL_START",
  TOOL_CALL_ARGS = "TOOL_CALL_ARGS",
  TOOL_CALL_END = "TOOL_CALL_END",

  // State
  STATE_SNAPSHOT = "STATE_SNAPSHOT",
  STATE_DELTA = "STATE_DELTA",
  MESSAGES_SNAPSHOT = "MESSAGES_SNAPSHOT",

  // Custom
  RAW = "RAW",
  CUSTOM = "CUSTOM",
}

Event Patterns

Start-Content-End: Streams content incrementally (text, tool arguments)
Snapshot-Delta: State synchronization using complete snapshots + JSON Patch updates
Lifecycle: Run monitoring with mandatory start/end events

Message Roles

user - User messages (text and multimodal)
assistant - AI responses (text and tool calls)
system - Instructions or context
tool - Tool execution results
activity - Progress updates
developer - Internal debugging

Tool Definition Structure

interface Tool {
  name: string;           // Unique identifier
  description: string;    // Purpose explanation
  parameters: JSONSchema; // Accepted arguments
}

Tool Call Lifecycle

TOOLCALLSTART - Initiates with unique ID
TOOLCALLARGS - Streams JSON arguments
TOOLCALLEND - Marks completion

State Synchronization

STATE_SNAPSHOT - Complete state replacement
STATE_DELTA - Incremental JSON Patch (RFC 6902) updates

Source

Documentation downloaded from: https://github.com/ag-ui-protocol/ag-ui/tree/main/docs

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