google__adk-docs/docs/agents/llm-agents.md

LLM Agent

Supported in ADKPython v0.1.0Go v0.1.0Java v0.1.0

The LlmAgent (often aliased simply as Agent) is a core component in ADK, acting as the "thinking" part of your application. It leverages the power of a Large Language Model (LLM) for reasoning, understanding natural language, making decisions, generating responses, and interacting with tools.

Unlike deterministic Workflow Agents that follow predefined execution paths, LlmAgent behavior is non-deterministic. It uses the LLM to interpret instructions and context, deciding dynamically how to proceed, which tools to use (if any), or whether to transfer control to another agent.

Building an effective LlmAgent involves defining its identity, clearly guiding its behavior through instructions, and equipping it with the necessary tools and capabilities.

Defining the Agent's Identity and Purpose

First, you need to establish what the agent is and what it's for.

• name (Required): Every agent needs a unique string identifier. This name is crucial for internal operations, especially in multi-agent systems where agents need to refer to or delegate tasks to each other. Choose a descriptive name that reflects the agent's function (e.g., customer_support_router, billing_inquiry_agent). Avoid reserved names like user.

• description (Optional, Recommended for Multi-Agent): Provide a concise summary of the agent's capabilities. This description is primarily used by other LLM agents to determine if they should route a task to this agent. Make it specific enough to differentiate it from peers (e.g., "Handles inquiries about current billing statements," not just "Billing agent").

• model (Required): Specify the underlying LLM that will power this agent's reasoning. This is a string identifier like "gemini-2.0-flash". The choice of model impacts the agent's capabilities, cost, and performance. See the Models page for available options and considerations.

=== "Python"

```python
# Example: Defining the basic identity
capital_agent = LlmAgent(
    model="gemini-2.0-flash",
    name="capital_agent",
    description="Answers user questions about the capital city of a given country."
    # instruction and tools will be added next
)
```

=== "Go"

```go
--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:identity"
```

=== "Java"

```java
// Example: Defining the basic identity
LlmAgent capitalAgent =
    LlmAgent.builder()
        .model("gemini-2.0-flash")
        .name("capital_agent")
        .description("Answers user questions about the capital city of a given country.")
        // instruction and tools will be added next
        .build();
```

Guiding the Agent: Instructions (instruction)

The instruction parameter is arguably the most critical for shaping an LlmAgent's behavior. It's a string (or a function returning a string) that tells the agent:

• Its core task or goal.
• Its personality or persona (e.g., "You are a helpful assistant," "You are a witty pirate").
• Constraints on its behavior (e.g., "Only answer questions about X," "Never reveal Y").
• How and when to use its tools. You should explain the purpose of each tool and the circumstances under which it should be called, supplementing any descriptions within the tool itself.
• The desired format for its output (e.g., "Respond in JSON," "Provide a bulleted list").

Tips for Effective Instructions:

• Be Clear and Specific: Avoid ambiguity. Clearly state the desired actions and outcomes.
• Use Markdown: Improve readability for complex instructions using headings, lists, etc.
• Provide Examples (Few-Shot): For complex tasks or specific output formats, include examples directly in the instruction.
• Guide Tool Use: Don't just list tools; explain when and why the agent should use them.

State:

• The instruction is a string template, you can use the {var} syntax to insert dynamic values into the instruction.
• {var} is used to insert the value of the state variable named var.
• {artifact.var} is used to insert the text content of the artifact named var.
• If the state variable or artifact does not exist, the agent will raise an error. If you want to ignore the error, you can append a ? to the variable name as in {var?}.

=== "Python"

```python
# Example: Adding instructions
capital_agent = LlmAgent(
    model="gemini-2.0-flash",
    name="capital_agent",
    description="Answers user questions about the capital city of a given country.",
    instruction="""You are an agent that provides the capital city of a country.
When a user asks for the capital of a country:
1. Identify the country name from the user's query.
2. Use the `get_capital_city` tool to find the capital.
3. Respond clearly to the user, stating the capital city.
Example Query: "What's the capital of {country}?"
Example Response: "The capital of France is Paris."
""",
    # tools will be added next
)
```

=== "Go"

```go
--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:instruction"
```

=== "Java"

```java
// Example: Adding instructions
LlmAgent capitalAgent =
    LlmAgent.builder()
        .model("gemini-2.0-flash")
        .name("capital_agent")
        .description("Answers user questions about the capital city of a given country.")
        .instruction(
            """
            You are an agent that provides the capital city of a country.
            When a user asks for the capital of a country:
            1. Identify the country name from the user's query.
            2. Use the `get_capital_city` tool to find the capital.
            3. Respond clearly to the user, stating the capital city.
            Example Query: "What's the capital of {country}?"
            Example Response: "The capital of France is Paris."
            """)
        // tools will be added next
        .build();
```

(Note: For instructions that apply to all agents in a system, consider using global_instruction on the root agent, detailed further in the Multi-Agents section.)

Equipping the Agent: Tools (tools)

Tools give your LlmAgent capabilities beyond the LLM's built-in knowledge or reasoning. They allow the agent to interact with the outside world, perform calculations, fetch real-time data, or execute specific actions.

• tools (Optional): Provide a list of tools the agent can use. Each item in the list can be:
  • A native function or method (wrapped as a FunctionTool). Python ADK automatically wraps the native function into a FuntionTool whereas, you must explicitly wrap your Java methods using FunctionTool.create(...)
  • An instance of a class inheriting from BaseTool.
  • An instance of another agent (AgentTool, enabling agent-to-agent delegation - see Multi-Agents).

The LLM uses the function/tool names, descriptions (from docstrings or the description field), and parameter schemas to decide which tool to call based on the conversation and its instructions.

=== "Python"

```python
# Define a tool function
def get_capital_city(country: str) -> str:
  """Retrieves the capital city for a given country."""
  # Replace with actual logic (e.g., API call, database lookup)
  capitals = {"france": "Paris", "japan": "Tokyo", "canada": "Ottawa"}
  return capitals.get(country.lower(), f"Sorry, I don't know the capital of {country}.")

# Add the tool to the agent
capital_agent = LlmAgent(
    model="gemini-2.0-flash",
    name="capital_agent",
    description="Answers user questions about the capital city of a given country.",
    instruction="""You are an agent that provides the capital city of a country... (previous instruction text)""",
    tools=[get_capital_city] # Provide the function directly
)
```

=== "Go"

```go
--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:tool_example"
```

=== "Java"

```java

// Define a tool function
// Retrieves the capital city of a given country.
public static Map<String, Object> getCapitalCity(
        @Schema(name = "country", description = "The country to get capital for")
        String country) {
  // Replace with actual logic (e.g., API call, database lookup)
  Map<String, String> countryCapitals = new HashMap<>();
  countryCapitals.put("canada", "Ottawa");
  countryCapitals.put("france", "Paris");
  countryCapitals.put("japan", "Tokyo");

  String result =
          countryCapitals.getOrDefault(
                  country.toLowerCase(), "Sorry, I couldn't find the capital for " + country + ".");
  return Map.of("result", result); // Tools must return a Map
}

// Add the tool to the agent
FunctionTool capitalTool = FunctionTool.create(experiment.getClass(), "getCapitalCity");
LlmAgent capitalAgent =
    LlmAgent.builder()
        .model("gemini-2.0-flash")
        .name("capital_agent")
        .description("Answers user questions about the capital city of a given country.")
        .instruction("You are an agent that provides the capital city of a country... (previous instruction text)")
        .tools(capitalTool) // Provide the function wrapped as a FunctionTool
        .build();
```

Learn more about Tools in the Tools section.

Advanced Configuration & Control

Beyond the core parameters, LlmAgent offers several options for finer control:

Configuring LLM Generation (generate_content_config)

You can adjust how the underlying LLM generates responses using generate_content_config.

• generate_content_config (Optional): Pass an instance of google.genai.types.GenerateContentConfig to control parameters like temperature (randomness), max_output_tokens (response length), top_p, top_k, and safety settings.

=== "Python"

```python
from google.genai import types

agent = LlmAgent(
    # ... other params
    generate_content_config=types.GenerateContentConfig(
        temperature=0.2, # More deterministic output
        max_output_tokens=250,
        safety_settings=[
            types.SafetySetting(
                category=types.HarmCategory.HARM_CATEGORY_DANGEROUS_CONTENT,
                threshold=types.HarmBlockThreshold.BLOCK_LOW_AND_ABOVE,
            )
        ]
    )
)
```

=== "Go"

```go
import "google.golang.org/genai"

--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:gen_config"
```

=== "Java"

```java
import com.google.genai.types.GenerateContentConfig;

LlmAgent agent =
    LlmAgent.builder()
        // ... other params
        .generateContentConfig(GenerateContentConfig.builder()
            .temperature(0.2F) // More deterministic output
            .maxOutputTokens(250)
            .build())
        .build();
```

Structuring Data (input_schema, output_schema, output_key)

For scenarios requiring structured data exchange with an LLM Agent, the ADK provides mechanisms to define expected input and desired output formats using schema definitions.

• input_schema (Optional): Define a schema representing the expected input structure. If set, the user message content passed to this agent must be a JSON string conforming to this schema. Your instructions should guide the user or preceding agent accordingly.

• output_schema (Optional): Define a schema representing the desired output structure. If set, the agent's final response must be a JSON string conforming to this schema.

• output_key (Optional): Provide a string key. If set, the text content of the agent's final response will be automatically saved to the session's state dictionary under this key. This is useful for passing results between agents or steps in a workflow.

  • In Python, this might look like: session.state[output_key] = agent_response_text
  • In Java: session.state().put(outputKey, agentResponseText)
  • In Golang, within a callback handler: ctx.State().Set(output_key, agentResponseText)

=== "Python"

The input and output schema is typically a `Pydantic` BaseModel.

```python
from pydantic import BaseModel, Field

class CapitalOutput(BaseModel):
    capital: str = Field(description="The capital of the country.")

structured_capital_agent = LlmAgent(
    # ... name, model, description
    instruction="""You are a Capital Information Agent. Given a country, respond ONLY with a JSON object containing the capital. Format: {"capital": "capital_name"}""",
    output_schema=CapitalOutput, # Enforce JSON output
    output_key="found_capital"  # Store result in state['found_capital']
    # Cannot use tools=[get_capital_city] effectively here
)
```

=== "Go"

The input and output schema is a `google.genai.types.Schema` object.

```go
--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:schema_example"
```

=== "Java"

 The input and output schema is a `google.genai.types.Schema` object.

```java
private static final Schema CAPITAL_OUTPUT =
    Schema.builder()
        .type("OBJECT")
        .description("Schema for capital city information.")
        .properties(
            Map.of(
                "capital",
                Schema.builder()
                    .type("STRING")
                    .description("The capital city of the country.")
                    .build()))
        .build();

LlmAgent structuredCapitalAgent =
    LlmAgent.builder()
        // ... name, model, description
        .instruction(
                "You are a Capital Information Agent. Given a country, respond ONLY with a JSON object containing the capital. Format: {\"capital\": \"capital_name\"}")
        .outputSchema(capitalOutput) // Enforce JSON output
        .outputKey("found_capital") // Store result in state.get("found_capital")
        // Cannot use tools(getCapitalCity) effectively here
        .build();
```

Managing Context (include_contents)

Control whether the agent receives the prior conversation history.

• include_contents (Optional, Default: 'default'): Determines if the contents (history) are sent to the LLM.
  • 'default': The agent receives the relevant conversation history.
  • 'none': The agent receives no prior contents. It operates based solely on its current instruction and any input provided in the current turn (useful for stateless tasks or enforcing specific contexts).

=== "Python"

```python
stateless_agent = LlmAgent(
    # ... other params
    include_contents='none'
)
```

=== "Go"

```go
import "google.golang.org/adk/agent/llmagent"

--8<-- "examples/go/snippets/agents/llm-agents/snippets/main.go:include_contents"
```

=== "Java"

```java
import com.google.adk.agents.LlmAgent.IncludeContents;

LlmAgent statelessAgent =
    LlmAgent.builder()
        // ... other params
        .includeContents(IncludeContents.NONE)
        .build();
```

Planner

Supported in ADKPython v0.1.0

planner (Optional): Assign a BasePlanner instance to enable multi-step reasoning and planning before execution. There are two main planners:

• BuiltInPlanner: Leverages the model's built-in planning capabilities (e.g., Gemini's thinking feature). See Gemini Thinking for details and examples.

  Here, the thinking_budget parameter guides the model on the number of thinking tokens to use when generating a response. The include_thoughts parameter controls whether the model should include its raw thoughts and internal reasoning process in the response.

  from google.adk import Agent
  from google.adk.planners import BuiltInPlanner
  from google.genai import types
  
  my_agent = Agent(
      model="gemini-2.5-flash",
      planner=BuiltInPlanner(
          thinking_config=types.ThinkingConfig(
              include_thoughts=True,
              thinking_budget=1024,
          )
      ),
      # ... your tools here
  )
  

• PlanReActPlanner: This planner instructs the model to follow a specific structure in its output: first create a plan, then execute actions (like calling tools), and provide reasoning for its steps. It's particularly useful for models that don't have a built-in "thinking" feature.

  from google.adk import Agent
  from google.adk.planners import PlanReActPlanner
  
  my_agent = Agent(
      model="gemini-2.0-flash",
      planner=PlanReActPlanner(),
      # ... your tools here
  )
  

  The agent's response will follow a structured format:

  [user]: ai news
  [google_search_agent]: /*PLANNING*/
  1. Perform a Google search for "latest AI news" to get current updates and headlines related to artificial intelligence.
  2. Synthesize the information from the search results to provide a summary of recent AI news.
  
  /*ACTION*/
  /*REASONING*/
  The search results provide a comprehensive overview of recent AI news, covering various aspects like company developments, research breakthroughs, and applications. I have enough information to answer the user's request.
  
  /*FINAL_ANSWER*/
  Here's a summary of recent AI news:
  ....
  

Code Execution

Supported in ADKPython v0.1.0

• code_executor (Optional): Provide a BaseCodeExecutor instance to allow the agent to execute code blocks found in the LLM's response. (See Tools/Built-in tools).

Example for using built-in-planner:

from dotenv import load_dotenv


import asyncio
import os

from google.genai import types
from google.adk.agents.llm_agent import LlmAgent
from google.adk.runners import Runner
from google.adk.sessions import InMemorySessionService
from google.adk.artifacts.in_memory_artifact_service import InMemoryArtifactService # Optional
from google.adk.planners import BasePlanner, BuiltInPlanner, PlanReActPlanner
from google.adk.models import LlmRequest

from google.genai.types import ThinkingConfig
from google.genai.types import GenerateContentConfig

import datetime
from zoneinfo import ZoneInfo

APP_NAME = "weather_app"
USER_ID = "1234"
SESSION_ID = "session1234"

def get_weather(city: str) -> dict:
    """Retrieves the current weather report for a specified city.

    Args:
        city (str): The name of the city for which to retrieve the weather report.

    Returns:
        dict: status and result or error msg.
    """
    if city.lower() == "new york":
        return {
            "status": "success",
            "report": (
                "The weather in New York is sunny with a temperature of 25 degrees"
                " Celsius (77 degrees Fahrenheit)."
            ),
        }
    else:
        return {
            "status": "error",
            "error_message": f"Weather information for '{city}' is not available.",
        }


def get_current_time(city: str) -> dict:
    """Returns the current time in a specified city.

    Args:
        city (str): The name of the city for which to retrieve the current time.

    Returns:
        dict: status and result or error msg.
    """

    if city.lower() == "new york":
        tz_identifier = "America/New_York"
    else:
        return {
            "status": "error",
            "error_message": (
                f"Sorry, I don't have timezone information for {city}."
            ),
        }

    tz = ZoneInfo(tz_identifier)
    now = datetime.datetime.now(tz)
    report = (
        f'The current time in {city} is {now.strftime("%Y-%m-%d %H:%M:%S %Z%z")}'
    )
    return {"status": "success", "report": report}

# Step 1: Create a ThinkingConfig
thinking_config = ThinkingConfig(
    include_thoughts=True,   # Ask the model to include its thoughts in the response
    thinking_budget=256      # Limit the 'thinking' to 256 tokens (adjust as needed)
)
print("ThinkingConfig:", thinking_config)

# Step 2: Instantiate BuiltInPlanner
planner = BuiltInPlanner(
    thinking_config=thinking_config
)
print("BuiltInPlanner created.")

# Step 3: Wrap the planner in an LlmAgent
agent = LlmAgent(
    model="gemini-2.5-pro-preview-03-25",  # Set your model name
    name="weather_and_time_agent",
    instruction="You are an agent that returns time and weather",
    planner=planner,
    tools=[get_weather, get_current_time]
)

# Session and Runner
session_service = InMemorySessionService()
session = session_service.create_session(app_name=APP_NAME, user_id=USER_ID, session_id=SESSION_ID)
runner = Runner(agent=agent, app_name=APP_NAME, session_service=session_service)

# Agent Interaction
def call_agent(query):
    content = types.Content(role='user', parts=[types.Part(text=query)])
    events = runner.run(user_id=USER_ID, session_id=SESSION_ID, new_message=content)

    for event in events:
        print(f"\nDEBUG EVENT: {event}\n")
        if event.is_final_response() and event.content:
            final_answer = event.content.parts[0].text.strip()
            print("\n🟢 FINAL ANSWER\n", final_answer, "\n")

call_agent("If it's raining in New York right now, what is the current temperature?")

Putting It Together: Example

??? "Code" Here's the complete basic capital_agent:

=== "Python"

    ```python
    --8<-- "examples/python/snippets/agents/llm-agent/capital_agent.py"
    ```

=== "Go"

    ```go
    --8<-- "examples/go/snippets/agents/llm-agents/main.go:full_code"
    ```

=== "Java"

    ```java
    --8<-- "examples/java/snippets/src/main/java/agents/LlmAgentExample.java:full_code"
    ```

(This example demonstrates the core concepts. More complex agents might incorporate schemas, context control, planning, etc.)

Related Concepts (Deferred Topics)

While this page covers the core configuration of LlmAgent, several related concepts provide more advanced control and are detailed elsewhere:

• Callbacks: Intercepting execution points (before/after model calls, before/after tool calls) using before_model_callback, after_model_callback, etc. See Callbacks.
• Multi-Agent Control: Advanced strategies for agent interaction, including planning (planner), controlling agent transfer (disallow_transfer_to_parent, disallow_transfer_to_peers), and system-wide instructions (global_instruction). See Multi-Agents.