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

# Model Context Protocol (MCP)

The [Model Context Protocol (MCP)](https://modelcontextprotocol.io/overview) is an open standard that defines how LLMs interact with external tools and services. Vision Agents supports MCP for function calling and connecting to external tool servers.

## How Vision Agents Uses MCP

Vision Agents provides two ways to give your agent access to tools:

1. **Function Registration** — Decorate Python functions to make them callable by the LLM
2. **MCP Servers** — Connect to local or remote servers that expose tools

Both approaches work with any LLM that supports function calling (OpenAI, Gemini, etc.) and with Realtime models.

## Function Registration

Use `@llm.register_function()` to make any Python function available to your agent:

```python theme={null}
from vision_agents.plugins import openai

llm = openai.LLM(model="gpt-5.4")

@llm.register_function(description="Get current weather for a location")
async def get_weather(location: str) -> dict:
    return {"location": location, "temperature": "22°C", "condition": "Sunny"}

# The LLM will automatically call get_weather() when relevant
response = await llm.simple_response("What's the weather like in London?")
```

## MCP Servers

Connect to MCP servers for access to external services:

```python theme={null}
from vision_agents.core.mcp import MCPServerRemote, MCPServerLocal
from vision_agents.core.agents import Agent

# Remote server (HTTP)
github_server = MCPServerRemote(
    url="https://api.githubcopilot.com/mcp/",
    headers={"Authorization": f"Bearer {token}"}
)

# Local server (stdio)
local_server = MCPServerLocal(command="uv run my_mcp_server.py")

# Connect to your agent
agent = Agent(
    edge=getstream.Edge(),
    llm=openai.LLM(model="gpt-5.4"),
    agent_user=User(name="Assistant", id="agent"),
    mcp_servers=[github_server, local_server]
)
```

When you add MCP servers to an agent, tools are automatically discovered and registered with the LLM.

## When to Use Each Approach

| Approach                  | Best For                                            |
| ------------------------- | --------------------------------------------------- |
| **Function Registration** | Simple tools, inline logic, prototyping             |
| **MCP Servers**           | External APIs, shared tooling, complex integrations |

You can combine both — register local functions while also connecting MCP servers.

<Note>
  For detailed examples including parameter types, custom function names, and real-world patterns, see the [MCP and Function Calling Guide](/guides/mcp-tool-calling).
</Note>