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

# Overview

> Extend an agent with function tools, MCP servers, and a knowledge base.

An AI agent can do more than chat. You can extend it with custom actions, external services, and a knowledge base so it can call APIs, query databases, or fetch facts and include the results in its replies.

There are three ways to extend an agent, and they work well together:

* **Function Tools** run your own code.
* **MCP** connects standardized external tool servers.
* **RAG** grounds answers in your own documents.

## Ways to Extend an Agent

<CardGroup cols={1}>
  <Card title="Function Tools" icon="wrench" href="/build/tools-and-capabilities/function-tools">
    Functions your agent calls to run custom logic, call APIs, or access state.
  </Card>
</CardGroup>

<CardGroup cols={1}>
  <Card title="MCP" icon="plug" href="/build/tools-and-capabilities/mcp">
    Attach Model Context Protocol servers to extend your agent with external tools.
  </Card>
</CardGroup>

<CardGroup cols={1}>
  <Card title="RAG" icon="database" href="/build/tools-and-capabilities/rag">
    Ground agent answers in a knowledge base with custom retrieval..
  </Card>
</CardGroup>

## What's Next

<CardGroup cols={3}>
  <Card title="Function Tools" icon="wrench" href="/build/tools-and-capabilities/function-tools">
    Add custom actions to your agent.
  </Card>

  <Card title="Creating an Agent" icon="robot" href="/build/creating-an-agent">
    Register the tools on an agent you define.
  </Card>

  <Card title="Run Your Agent" icon="play" href="/build/run-the-runtime">
    Run the tool-equipped agent in a live session.
  </Card>
</CardGroup>

## References

<Tabs>
  <Tab title="Python">
    #### Examples

    <CardGroup cols={2}>
      <Card title="Tool Chaining" icon="github" href="https://github.com/ZeroRuntimeAI/zrt-python-sdk-examples/blob/main/features/function_tools.py">
        Chain multiple function tools in one turn.
      </Card>

      <Card title="MCP Integration" icon="github" href="https://github.com/ZeroRuntimeAI/zrt-python-sdk-examples/blob/main/features/mcp_tools.py">
        Connect tools through an MCP server.
      </Card>
    </CardGroup>

    #### SDK Reference

    <CardGroup cols={2}>
      <Card title="MCP" icon="plug" href="/api-reference/python/core/tools-and-mcp">
        `MCP` in the Python API reference.
      </Card>
    </CardGroup>
  </Tab>
</Tabs>