# Agent Class

The `Agent` class is the foundation for creating AI agents in Mastra. It provides methods for generating responses, streaming interactions, and handling voice capabilities.

## Usage examples

### Basic string instructions

```typescript
import { Agent } from "@mastra/core/agent";

// String instructions
export const agent = new Agent({
  id: "test-agent",
  name: "Test Agent",
  instructions: "You are a helpful assistant that provides concise answers.",
  model: "openai/gpt-5.1",
});

// System message object
export const agent2 = new Agent({
  id: "test-agent-2",
  name: "Test Agent 2",
  instructions: {
    role: "system",
    content: "You are an expert programmer",
  },
  model: "openai/gpt-5.1",
});

// Array of system messages
export const agent3 = new Agent({
  id: "test-agent-3",
  name: "Test Agent 3",
  instructions: [
    { role: "system", content: "You are a helpful assistant" },
    { role: "system", content: "You have expertise in TypeScript" },
  ],
  model: "openai/gpt-5.1",
});
```

### Single CoreSystemMessage

Use CoreSystemMessage format to access additional properties like `providerOptions` for provider-specific configurations:

```typescript
import { Agent } from "@mastra/core/agent";

export const agent = new Agent({
  id: "core-message-agent",
  name: "Core Message Agent",
  instructions: {
    role: "system",
    content:
      "You are a helpful assistant specialized in technical documentation.",
    providerOptions: {
      openai: {
        reasoningEffort: "low",
      },
    },
  },
  model: "openai/gpt-5.1",
});
```

### Multiple CoreSystemMessages

```typescript
import { Agent } from "@mastra/core/agent";

// This could be customizable based on the user
const preferredTone = {
  role: "system",
  content: "Always maintain a professional and empathetic tone.",
};

export const agent = new Agent({
  id: "multi-message-agent",
  name: "Multi Message Agent",
  instructions: [
    { role: "system", content: "You are a customer service representative." },
    preferredTone,
    {
      role: "system",
      content: "Escalate complex issues to human agents when needed.",
      providerOptions: {
        anthropic: { cacheControl: { type: "ephemeral" } },
      },
    },
  ],
  model: "anthropic/claude-sonnet-4-20250514",
});
```

## Constructor parameters

**id?:** (`string`): Unique identifier for the agent. Defaults to \`name\` if not provided.

**name:** (`string`): Display name for the agent. Used as the identifier if \`id\` is not provided.

**description?:** (`string`): Optional description of the agent's purpose and capabilities.

**instructions:** (`SystemMessage | ({ requestContext: RequestContext }) => SystemMessage | Promise<SystemMessage>`): Instructions that guide the agent's behavior. Can be a string, array of strings, system message object, array of system messages, or a function that returns any of these types dynamically. SystemMessage types: string | string\[] | CoreSystemMessage | CoreSystemMessage\[] | SystemModelMessage | SystemModelMessage\[]

**model:** (`MastraLanguageModel | ({ requestContext: RequestContext }) => MastraLanguageModel | Promise<MastraLanguageModel>`): The language model used by the agent. Can be provided statically or resolved at runtime.

**agents?:** (`Record<string, Agent> | ({ requestContext: RequestContext }) => Record<string, Agent> | Promise<Record<string, Agent>>`): Sub-Agents that the agent can access. Can be provided statically or resolved dynamically.

**tools?:** (`ToolsInput | ({ requestContext: RequestContext }) => ToolsInput | Promise<ToolsInput>`): Tools that the agent can access. Can be provided statically or resolved dynamically.

**workflows?:** (`Record<string, Workflow> | ({ requestContext: RequestContext }) => Record<string, Workflow> | Promise<Record<string, Workflow>>`): Workflows that the agent can execute. Can be static or dynamically resolved.

**defaultOptions?:** (`AgentExecutionOptions | ({ requestContext: RequestContext }) => AgentExecutionOptions | Promise<AgentExecutionOptions>`): Default options used when calling \`stream()\` and \`generate()\`.

**defaultGenerateOptionsLegacy?:** (`AgentGenerateOptions | ({ requestContext: RequestContext }) => AgentGenerateOptions | Promise<AgentGenerateOptions>`): Default options used when calling \`generateLegacy()\`.

**defaultStreamOptionsLegacy?:** (`AgentStreamOptions | ({ requestContext: RequestContext }) => AgentStreamOptions | Promise<AgentStreamOptions>`): Default options used when calling \`streamLegacy()\`.

**mastra?:** (`Mastra`): Reference to the Mastra runtime instance (injected automatically).

**scorers?:** (`MastraScorers | ({ requestContext: RequestContext }) => MastraScorers | Promise<MastraScorers>`): Scoring configuration for runtime evaluation and telemetry. Can be static or dynamically provided.

**memory?:** (`MastraMemory | ({ requestContext: RequestContext }) => MastraMemory | Promise<MastraMemory>`): Memory module used for storing and retrieving stateful context.

**voice?:** (`CompositeVoice`): Voice settings for speech input and output.

**inputProcessors?:** (`(Processor | ProcessorWorkflow)[] | ({ requestContext: RequestContext }) => (Processor | ProcessorWorkflow)[] | Promise<(Processor | ProcessorWorkflow)[]>`): Input processors that can modify or validate messages before they are processed by the agent. Can be individual Processor objects or workflows created with \`createWorkflow()\` using ProcessorStepSchema.

**outputProcessors?:** (`(Processor | ProcessorWorkflow)[] | ({ requestContext: RequestContext }) => (Processor | ProcessorWorkflow)[] | Promise<(Processor | ProcessorWorkflow)[]>`): Output processors that can modify or validate messages from the agent before they are sent to the client. Can be individual Processor objects or workflows.

**maxProcessorRetries?:** (`number`): Maximum number of times a processor can request retrying the LLM step.

**requestContextSchema?:** (`z.ZodType<any>`): Zod schema for validating request context values. When provided, the context is validated at the start of generate() or stream(), throwing a MastraError if validation fails.

## Returns

**agent:** (`Agent<TAgentId, TTools>`): A new Agent instance with the specified configuration.

## Related

- [Agents overview](https://mastra.ai/docs/agents/overview)