> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/agentclientprotocol/typescript-sdk/llms.txt
> Use this file to discover all available pages before exploring further.

# Types Overview

> Overview of the ACP TypeScript SDK type system

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.

## 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

## Importing Types

All types are exported from the schema module:

```typescript theme={null}
import type {
  InitializeRequest,
  InitializeResponse,
  NewSessionRequest,
  PromptRequest,
  SessionUpdate
} from '@agentclientprotocol/sdk/schema';
```

## Type Categories

The type system is organized into several categories:

### Request Types

Types for requests sent from client to agent. See [Request Types](/api/request-types) for details.

* `InitializeRequest`
* `NewSessionRequest`
* `LoadSessionRequest`
* `PromptRequest`
* `SetSessionModeRequest`
* And more...

### Response Types

Types for responses from agent to client. See [Response Types](/api/response-types) for details.

* `InitializeResponse`
* `NewSessionResponse`
* `PromptResponse`
* `ListSessionsResponse`
* And more...

### Notification Types

Types for one-way notifications. See [Notification Types](/api/notification-types) for details.

* `SessionNotification`
* `SessionUpdate` (union type)
* `CancelNotification`
* `CancelRequestNotification`

### 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

### 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

### Session Types

Types for session management:

* `SessionId` - Unique session identifier
* `SessionInfo` - Session metadata
* `SessionMode` - Session mode configuration
* `SessionConfigOption` - Configuration options

## Schema Constants

The SDK exports important constants. See [Schema Constants](/api/schema-constants) for details.

```typescript theme={null}
import { PROTOCOL_VERSION, AGENT_METHODS, CLIENT_METHODS } from '@agentclientprotocol/sdk/schema';
```

## Zod Validation

All types include corresponding Zod schemas for runtime validation:

```typescript theme={null}
import { InitializeRequestSchema } from '@agentclientprotocol/sdk/schema';

const result = InitializeRequestSchema.parse(data);
```

## Extensibility

All protocol types include an optional `_meta` field for custom metadata:

```typescript theme={null}
export type InitializeRequest = {
  _meta?: {
    [key: string]: unknown;
  } | null;
  // ... other fields
};
```

This allows both clients and agents to attach additional information without breaking protocol compatibility.

## Next Steps

* Explore [Request Types](/api/request-types)
* Learn about [Response Types](/api/response-types)
* Understand [Notification Types](/api/notification-types)
* Check [Schema Constants](/api/schema-constants)