> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agenticenv.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Response Format

> Configure plain-text or JSON schema structured output from the LLM using ResponseFormat

By default the agent uses **text-only** output. Use [`WithResponseFormat`](/getting-started/configuration) to request structured output — for example JSON with a schema the model must follow.

## Default (text)

Omit `WithResponseFormat` — the LLM responds as plain text:

```go theme={null}
a, err := agent.NewAgent(
    agent.WithLLMClient(llmClient),
    agent.WithSystemPrompt("You are a helpful assistant."),
    // No WithResponseFormat — text output
)
```

Force text explicitly when you need to reset a previously set format:

```go theme={null}
agent.WithResponseFormat(&interfaces.ResponseFormat{
    Type: interfaces.ResponseFormatText,
})
```

## JSON with schema

Use `interfaces.ResponseFormatJSON` with a valid JSON Schema. The root must be `type: "object"` with `properties`:

```go theme={null}
import "github.com/agenticenv/agent-sdk-go/pkg/interfaces"

a, err := agent.NewAgent(
    agent.WithLLMClient(llmClient),
    agent.WithResponseFormat(&interfaces.ResponseFormat{
        Type: interfaces.ResponseFormatJSON,
        Name: "AgentResponse",
        Schema: interfaces.JSONSchema{
            "type": "object",
            "properties": interfaces.JSONSchema{
                "response":   interfaces.JSONSchema{"type": "string"},
                "confidence": interfaces.JSONSchema{"type": "number"},
            },
            "required": []any{"response"},
        },
    }),
)
```

The schema is sent to the LLM on every request for that agent. Parse `result.Content` as JSON in your application.

<Note>
  The schema root must be `type: "object"`. Primitive or array roots are not valid JSON Schema for Structured Outputs.
</Note>

## Provider support

Structured Outputs (JSON schema enforcement) require models that support it — for example `gpt-4o` and `gpt-4o-mini` on OpenAI. Older models may fall back to JSON mode without strict schema enforcement.

<Warning>
  Response format is part of the static agent spec. Include the **same** `WithResponseFormat` on both `NewAgent` and `NewAgentWorker` when using split processes — it participates in the fingerprint check.
</Warning>

## Example

<CardGroup cols={2}>
  <Card title="JSON Response" icon="play" href="/examples/json-response">
    Structured output with response format
  </Card>
</CardGroup>

## Related

<CardGroup cols={2}>
  <Card title="LLM Providers" icon="robot" href="/getting-started/llm-providers">
    OpenAI, Anthropic, and Gemini clients
  </Card>

  <Card title="Reasoning" icon="lightbulb" href="/features/reasoning">
    Extended thinking alongside structured output
  </Card>

  <Card title="Configuration" icon="sliders" href="/getting-started/configuration">
    WithResponseFormat reference
  </Card>

  <Card title="Tools" icon="wrench" href="/features/tools">
    Combine structured output with tool use
  </Card>
</CardGroup>