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### What “Fast‑MCP” is today – and why your code keeps breaking
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| What you tried to import | Why it fails | What to do instead |
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|---|---|---|
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| `from fastmcp.servers …` / `fastmcp.client.sse` | **The layout you remember was removed.**<br/>As of *FastMCP ≥ 1.0* the project focuses **only on helping you *write servers***. All *client‑side* helpers (SSE transport, `FastClientSession`, etc.) were merged into the **official `mcp` Python SDK** and deleted from FastMCP. citeturn14view0 | • Keep using the **`mcp` SDK** for talking to servers (list tools, call tools).<br/>• Use **FastMCP only to *build* servers you want to expose to Claude/Swarms**. |
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| `NotRequired` from `typing` on Python ≤ 3.10 | `typing.NotRequired` is available only in 3.11+. | Import it from `typing_extensions`: <br/>```python<br/>from typing_extensions import NotRequired, TypedDict<br/>``` |
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---
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## 1 · Update your Swarms integration (client side)
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```diff
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- from fastmcp.client.sse import sse_client
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- from fastmcp import FastClientSession as ClientSession
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+ from mcp import ClientSession # unchanged from old codebase
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+ from mcp.client.sse import sse_client # still lives in `mcp`
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```
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Nothing else in your `MCPServer*` helper classes has to change – the wire protocol is the same.
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### Add the missing `mcp_servers` field to `Agent`
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```diff
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class Agent:
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def __init__(self,
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...
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- tools_list_dictionary: Optional[List[Dict[str, Any]]] = None,
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+ tools_list_dictionary: Optional[List[Dict[str, Any]]] = None,
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+ mcp_servers: Optional[list[MCPServerSseParams]] = None,
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*args, **kwargs):
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...
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self.mcp_servers = mcp_servers or []
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```
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and inside `handle_tool_init` gate tool execution with `if self.mcp_servers:` instead of accessing an attribute that did not exist.
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---
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## 2 · Build (or re‑use) servers with FastMCP
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FastMCP is perfect for *authoring* a server – e.g. a tiny calculator you can smoke‑test against Swarms:
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```python
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# calc_server.py
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from fastmcp import FastMCP
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mcp = FastMCP("Calc") # the object name *must* be `mcp`, `app`, or `server`
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@mcp.tool()
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def add(a: int, b: int) -> int:
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"""Add two numbers"""
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return a + b
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```
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Run it locally:
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```bash
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pip install fastmcp mcp # FastMCP 2.2.0 pulls the right deps
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fastmcp dev calc_server.py # opens the GUI inspector
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```
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or keep it running for Swarms with
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```bash
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fastmcp run calc_server.py
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```
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---
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## 3 · Connect from Swarms (smoke‑test)
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```python
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from swarms import Agent
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from swarms.tools.mcp_integration import MCPServerSseParams
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server_local = MCPServerSseParams(
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url="http://127.0.0.1:6274", # the URL printed by `fastmcp run`
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headers={"Content-Type": "application/json"},
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)
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agent = Agent(
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agent_name = "Math‑Smoke‑Tester",
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system_prompt = "You call external MCP tools to do the math.",
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mcp_servers = [server_local], # <-- now it exists
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max_loops = 1,
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)
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print(agent.run("Use the add tool to add 2 and 2"))
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```
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If the calculator server is reachable, Swarms will:
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1. Receive the LLM’s function‑call JSON,
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2. Pass it to `batch_mcp_flow`,
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3. The MCP client will POST to `http://127.0.0.1:6274`,
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4. Tool returns `4`, which your `Agent` prints.
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---
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## 4 · Where to read the current docs
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* **FastMCP PyPI** – installation & quick‑start citeturn14view0
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* **Official MCP SDK** (client utilities) – <https://github.com/modelcontextprotocol/python-sdk>
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Stick to this split and you can forget about missing modules or mismatched versions. |
