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The ACP TypeScript SDK provides comprehensive type definitions for the Agent Client Protocol. All types are auto-generated from the protocol specification using OpenAPI and validated with Zod schemas.

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Type System

The SDK’s type system is built on three key principles:
  1. Auto-generated: Types are generated from the OpenAPI specification to ensure accuracy and consistency with the protocol
  2. Zod validation: All types include Zod schemas for runtime validation
  3. TypeScript-first: Full TypeScript support with strict typing throughout

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Importing Types

All types are exported from the schema module: 
import type {
  InitializeRequest,
  InitializeResponse,
  NewSessionRequest,
  PromptRequest,
  SessionUpdate
} from '@agentclientprotocol/sdk/schema';

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Type Categories

The type system is organized into several categories:

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Request Types

Types for requests sent from client to agent. See Request Types for details.
  • InitializeRequest
  • NewSessionRequest
  • LoadSessionRequest
  • PromptRequest
  • SetSessionModeRequest
  • And more…

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Response Types

Types for responses from agent to client. See Response Types for details.
  • InitializeResponse
  • NewSessionResponse
  • PromptResponse
  • ListSessionsResponse
  • And more…

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Notification Types

Types for one-way notifications. See Notification Types for details.
  • SessionNotification
  • SessionUpdate (union type)
  • CancelNotification
  • CancelRequestNotification

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Content Types

Types for representing content in messages:
  • ContentBlock - Union of text, image, audio, resource link, or embedded resource
  • TextContent - Plain text content
  • ImageContent - Image data with MIME type
  • AudioContent - Audio data with MIME type
  • ResourceLink - Reference to a resource
  • EmbeddedResource - Embedded resource content

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Capability Types

Types for negotiating features between client and agent:
  • ClientCapabilities - What the client supports
  • AgentCapabilities - What the agent supports
  • PromptCapabilities - Supported content types in prompts
  • FileSystemCapabilities - File system operations
  • McpCapabilities - MCP transport support

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Session Types

Types for session management:
  • SessionId - Unique session identifier
  • SessionInfo - Session metadata
  • SessionMode - Session mode configuration
  • SessionConfigOption - Configuration options

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Schema Constants

The SDK exports important constants. See Schema Constants for details. 
import { PROTOCOL_VERSION, AGENT_METHODS, CLIENT_METHODS } from '@agentclientprotocol/sdk/schema';

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Zod Validation

All types include corresponding Zod schemas for runtime validation: 
import { InitializeRequestSchema } from '@agentclientprotocol/sdk/schema';

const result = InitializeRequestSchema.parse(data);

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Extensibility

All protocol types include an optional _meta field for custom metadata: 
export type InitializeRequest = {
  _meta?: {
    [key: string]: unknown;
  } | null;
  // ... other fields
};
This allows both clients and agents to attach additional information without breaking protocol compatibility.

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