Structured outputs

Structured Outputs vs. JSON Mode

When working with language models, generating responses that match a specific structure is crucial for building reliable applications. Agno Agents support two methods to achieve this: Structured Outputs and JSON mode.

Structured Outputs (Default if supported)

“Structured Outputs” is the preferred and most reliable way to extract well-formed, schema-compliant responses from a Model. If a model class supports it, Agno Agents use Structured Outputs by default.

With structured outputs, we provide a schema to the model (using Pydantic or JSON Schema), and the model’s response is guaranteed to strictly follow that schema. This eliminates many common issues like missing fields, invalid enum values, or inconsistent formatting. Structured Outputs are ideal when you need high-confidence, well-structured responses—like entity extraction, content generation for UI rendering, and more.

In this case, the response model is passed as a keyword argument to the model.

Example

from pydantic import BaseModel
from agno.agent import Agent
from agno.models.openai import OpenAIChat

class User(BaseModel):
    name: str
    age: int
    email: str

agent = Agent(
    model=OpenAIChat(id="gpt-4o"),
    description="You are a helpful assistant that can extract information from a user's profile.",
    response_model=User,
)

In the example above, the model will generate a response that matches the User schema using structured outputs via OpenAI’s gpt-4o model. The agent will then return the User object as-is.

JSON Mode

Some model classes do not support Structured Outputs, or you may want to fall back to JSON mode even when the model supports both options. In such cases, you can enable JSON mode by setting use_json_mode=True.

JSON mode works by injecting a detailed description of the expected JSON structure into the system prompt. The model is then instructed to return a valid JSON object that follows this structure. Unlike Structured Outputs, the response is not automatically validated against the schema at the API level.

Example

from pydantic import BaseModel
from agno.agent import Agent
from agno.models.openai import OpenAIChat

class User(BaseModel):
    name: str
    age: int
    email: str

agent = Agent(
    model=OpenAIChat(id="gpt-4o"),
    description="You are a helpful assistant that can extract information from a user's profile.",
    response_model=User,
    use_json_mode=True,
)

When to use

Use Structured Outputs if the model supports it — it’s reliable, clean, and validated automatically.

Use JSON mode:

When the model doesn’t support structured outputs. Agno agents do this by default on your behalf.
When you need broader compatibility, but are okay validating manually.
When the model does not support tools with structured outputs.

FAQs