Test MCP-Use SDK Based Apps

What mcp-use IS vs. What It Is NOT

	mcp-use (`pip install mcp-use`)	MCP Server SDK (`pip install mcp`)	Claude Agent SDK	mcp-use Server SDK (TS/Python)
Purpose	Connect a LangChain LLM to one or more existing MCP servers	Build / expose an MCP server	Build agents using Anthropic's agent framework	Build production MCP servers with built-in transport, sessions, OAuth
Key classes	`MCPClient`, `MCPAgent`, `MCPSession`	`Server`, `StdioServerTransport`	`@tool` decorator, `createSdkMcpServer`	`MCPServer`, `text()`, `object()`, session stores, OAuth providers
Tool relationship	Discovers tools from running servers	Defines tools that servers expose	Defines tools for the agent to use	Defines tools via `server.tool()` / `@server.tool()` decorators
Import	`from mcp_use import MCPClient, MCPAgent`	`from mcp.server import Server`	N/A (TypeScript SDK)	TS: `import { MCPServer } from 'mcp-use/server'` / Python: `from mcp_use import MCPServer`
Config	`{"mcpServers": {"name": {…}}}` dict	N/A — you write the server code	N/A	Server config object with name, version, sessionStore, OAuth

Rule of thumb: If the file consumes MCP tools, it should import from mcp_use (client). If it provides MCP tools, it can import from mcp.server (official SDK) or mcp-use/server (mcp-use Server SDK, which wraps the official SDK with production features). Mixing client and server imports in the same file is almost always wrong.

Server Config Schema

The config dict follows the Claude Desktop / Cursor convention. Transport type is auto-detected by key presence.

Stdio (command-based)

{
  "mcpServers": {
    "server-name": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "."],
      "env": { "SOME_VAR": "value" }
    }
  }
}

Detected when the server entry has a "command" key → StdioConnector.

HTTP / SSE / Streamable HTTP

{
  "mcpServers": {
    "remote-server": {
      "url": "http://localhost:3000/mcp",
      "headers": { "Authorization": "Bearer token" },
      "timeout": 5,
      "sse_read_timeout": 300
    }
  }
}

Detected when the server entry has a "url" key → HttpConnector (auto-negotiates Streamable HTTP first, falls back to SSE).

WebSocket

{
  "mcpServers": {
    "ws-server": {
      "ws_url": "ws://localhost:8080/mcp"
    }
  }
}

Detected when the server entry has a "ws_url" key → WebSocketConnector.

Loading the config

# From dict
client = MCPClient(config={"mcpServers": {…}})

# From JSON file path
client = MCPClient(config="path/to/config.json")

# Factory methods
client = MCPClient.from_dict(config_dict)
client = MCPClient.from_config_file("config.json")

Correct Client Lifecycle

High-level (MCPAgent — most common)

import asyncio
from langchain_openai import ChatOpenAI
from mcp_use import MCPAgent, MCPClient

async def main():
    client = MCPClient(config={"mcpServers": {…}})        # 1. parse config (sync)
    llm = ChatOpenAI(model="gpt-4o")                       # 2. create LLM (sync)
    agent = MCPAgent(llm=llm, client=client, max_steps=30) # 3. create agent (sync)
    result = await agent.run("Do something")                # 4. run (async) — connects, discovers tools, runs loop
    print(result)

asyncio.run(main())

agent.run() handles the entire lifecycle: connect → initialize → discover tools → run agent loop → return result.

Low-level (MCPClient direct usage)

async def main():
    client = MCPClient(config=config)                            # 1. parse config
    await client.create_all_sessions()                           # 2. connect to all servers (ASYNC)
    session = client.get_session("server-name")                  # 3. get session (sync)
    tools = await session.list_tools()                           # 4. list tools (ASYNC)
    result = await session.call_tool("tool-name", {"arg": "v"})  # 5. call tool (ASYNC)
    await client.close_all_sessions()                            # 6. cleanup (ASYNC)

MCPSession as context manager

async with MCPSession(connector=some_connector) as session:
    await session.initialize()
    tools = await session.list_tools()
    result = await session.call_tool("tool-name", {"arg": "v"})

What requires async/await

Operation	Async?	Notes
`MCPClient(config=…)`	No	Just parses config
`MCPClient.from_dict(…)`	No	Just parses config
`MCPAgent(llm=…, client=…)`	No	Just stores references
`agent.run(query)`	Yes	Full lifecycle
`agent.initialize()`	Yes	Connects + discovers tools
`client.create_session(name)`	Yes	Connects to one server
`client.create_all_sessions()`	Yes	Connects to all servers
`session.list_tools()`	Yes	MCP protocol call
`session.call_tool(name, args)`	Yes	MCP protocol call
`client.close_all_sessions()`	Yes	Disconnects all

6 AI Derailment Patterns

Pattern 1: Server SDK vs. Client SDK Conflation

AI writes:

from mcp.server import Server
from mcp.server.stdio import StdioServerTransport

server = Server("my-app")

@server.tool()
def search(query: str) -> str:
    ...

…in a file that should be consuming tools from an existing MCP server.

Why it fails: mcp.server.Server creates a new MCP server. The app needs mcp_use.MCPClient to connect to an already-running server and discover its tools.

Detect it:

grep for "from mcp.server import" or "StdioServerTransport" in files that also import from mcp_use or reference mcpServers config

Fix:

from mcp_use import MCPClient, MCPAgent

client = MCPClient(config={"mcpServers": {"server-name": {"command": "…", "args": […]}}})
agent = MCPAgent(llm=llm, client=client)
result = await agent.run("query")

Pattern 2: Claude Agent SDK @tool Decorator Misapplication

AI writes:

from mcp_use import MCPClient
# Then also tries:
from some_sdk import tool  # or uses @tool decorator

@tool
def search_listings(query: str):
    """Search for listings."""
    ...

# Attempts to register hand-written tools with mcp-use

Why it fails: mcp-use discovers tools from running MCP servers — it does not accept user-defined tool functions. The @tool decorator pattern belongs to frameworks that define tools locally (like Claude Agent SDK or LangChain's @tool). In mcp-use, tools are defined in the MCP server, not in the consumer.

Detect it:

grep for "@tool" decorator in files that import from mcp_use
grep for "createSdkMcpServer" in any Python file

Fix:

# Tools come FROM the MCP server, not from your code
client = MCPClient(config={"mcpServers": {"my-server": {"command": "…", "args": […]}}})
agent = MCPAgent(llm=llm, client=client)
# The agent will automatically discover all tools exposed by the server
result = await agent.run("search for listings in Barcelona")

Pattern 3: Tool Schema Field Name Mismatch

AI writes:

# OpenAI-style schema
tool_def = {
    "name": "search",
    "parameters": {  # ← WRONG key
        "type": "object",
        "properties": {"query": {"type": "string"}}
    }
}

# Or TypeScript SDK style
tool_def = {
    "name": "search",
    "inputSchema": {…}  # Correct MCP key, but wrong context — you shouldn't be defining tools
}

Why it fails: MCP tools use inputSchema (camelCase) in the protocol. But with mcp-use, you don't define tool schemas at all — tools are discovered from servers. The mcp.types.Tool objects returned by session.list_tools() have name, description, and inputSchema attributes. If the agent is writing tool schema dicts, it has fundamentally misunderstood mcp-use's role.

Detect it:

grep for "parameters" adjacent to tool definitions in mcp_use consumer files
grep for manual Tool() construction or tool schema dicts in consumer code

Fix:

# Don't define schemas — discover them
session = client.get_session("server-name")
tools = await session.list_tools()  # Returns list[mcp.types.Tool]
for tool in tools:
    print(tool.name)          # str
    print(tool.description)   # str
    print(tool.inputSchema)   # dict (JSON Schema)

Pattern 4: Missing Async Lifecycle Steps

AI writes:

from mcp_use import MCPClient

client = MCPClient(config=config)
session = client.get_session("server")  # ← CRASH: no sessions created yet
tools = session.list_tools()            # ← Missing await

Why it fails: MCPClient(config=…) only parses the config — it does NOT connect to servers. You must call await client.create_session("name") or await client.create_all_sessions() before accessing sessions. Also, list_tools() is async and requires await. When using MCPAgent, the agent.run() method handles this automatically.

Detect it:

grep for "client.get_session" not preceded by "await client.create" in the same function
grep for "session.list_tools()" or "session.call_tool(" without "await" prefix
grep for mcp_use usage outside an async function

Fix:

# Option A: Let MCPAgent handle it (recommended)
agent = MCPAgent(llm=llm, client=client)
result = await agent.run("query")  # Handles connect + discover + run

# Option B: Manual lifecycle
client = MCPClient(config=config)
await client.create_all_sessions()          # ← MUST await this first
session = client.get_session("server")
tools = await session.list_tools()          # ← MUST await
result = await session.call_tool("name", {"arg": "val"})  # ← MUST await
await client.close_all_sessions()           # ← Cleanup

Pattern 5: Tool Name Format Incompatibility

AI writes:

# Assumes tools are namespaced
result = await session.call_tool("server-name.search", {"query": "test"})

# Or uses dots in tool names with OpenAI
# → Error: string does not match pattern '^[a-zA-Z0-9_-]+$'

Why it fails: mcp-use exposes tools with their original names from the MCP server — no namespace prefix is added. A tool named search on the server is just search, not server-name.search. However, some MCP servers expose tool names containing dots (e.g., prometheus.execute_query), which breaks OpenAI's tool name validation regex.

Detect it:

grep for "call_tool" with dot-separated names like "server.tool"
grep for "Invalid.*function.name.*pattern" in error logs

Fix:

# Tools use their original server names — no prefix
tools = await session.list_tools()
print([t.name for t in tools])  # e.g., ["search", "get_details", "add"]

# Call by original name
result = await session.call_tool("search", {"query": "test"})

# If a server exposes dotted names and you use OpenAI, sanitize:
# Replace dots with underscores or use a different LLM provider

Pattern 6: LangChain Import Path / Version Mismatch

AI writes:

# Old-style imports (pre-LangChain 1.0)
from langchain.llms import OpenAI              # ← DEPRECATED path
from langchain.chat_models import ChatOpenAI   # ← DEPRECATED path
from langchain.agents import initialize_agent   # ← REMOVED in 1.0

# Or wrong package
from langchain import ChatOpenAI  # ← Not valid

Why it fails: mcp-use requires langchain>=1.0.0. In LangChain 1.0+, LLM providers moved to separate packages (langchain-openai, langchain-anthropic, etc.). The old langchain.llms and langchain.chat_models paths are removed or deprecated. Also, initialize_agent was replaced by create_agent (from LangGraph).

Detect it:

grep for "from langchain.llms" or "from langchain.chat_models" in files using mcp_use
grep for "initialize_agent" in files using mcp_use
grep for "from langchain import Chat" (wrong path)

Fix:

# Correct imports for LangChain 1.0+
from langchain_openai import ChatOpenAI           # pip install langchain-openai
from langchain_anthropic import ChatAnthropic     # pip install langchain-anthropic
from langchain_google_genai import ChatGoogleGenerativeAI  # pip install langchain-google-genai

# mcp-use handles agent creation internally — don't use initialize_agent
from mcp_use import MCPAgent, MCPClient

agent = MCPAgent(llm=ChatOpenAI(model="gpt-4o"), client=client)
result = await agent.run("query")

Review Checklist

Run these checks against any mcp-use codebase. Each item is verifiable via grep or file inspection.

Import Correctness

RC-01: No from mcp.server import Server in consumer/client files
RC-02: No StdioServerTransport import in consumer/client files
RC-03: No @tool decorator used alongside mcp_use imports
RC-04: No from langchain.llms import (deprecated path)
RC-05: No from langchain.chat_models import (deprecated path)
RC-06: No initialize_agent usage (removed in LangChain 1.0)
RC-07: LLM imports use provider packages (langchain_openai, langchain_anthropic, etc.)

Config Correctness

RC-08: Config dict has top-level "mcpServers" key (not "servers" or "mcp_servers")
RC-09: Stdio servers have both "command" and "args" keys
RC-10: HTTP servers use "url" key (not "endpoint" or "base_url")
RC-11: WebSocket servers use "ws_url" key (not "websocket" or "ws")

Async Correctness

RC-12: All mcp-use operations run inside async def functions
RC-13: agent.run() is awaited
RC-14: client.create_session() / client.create_all_sessions() is awaited before accessing sessions
RC-15: session.list_tools() and session.call_tool() are awaited
RC-16: Entry point uses asyncio.run(main()) (not bare main())

Lifecycle Correctness

RC-17: client.get_session() is not called before create_session() or create_all_sessions()
RC-18: client.close_all_sessions() is called in cleanup (or try/finally block)
RC-19: When using MCPSession directly, it uses async with or explicit connect()/disconnect()

Tool Usage

RC-20: No manual tool schema definitions (parameters: dicts) in consumer code
RC-21: Tool calls use original server names (no fabricated namespaced names)
RC-22: No Tool() constructor calls in consumer code (tools come from list_tools())

Test Patterns

Mocking an MCP Server for Unit Tests

import pytest
import pytest_asyncio
from unittest.mock import AsyncMock, MagicMock, patch
from mcp.types import Tool, CallToolResult, TextContent

@pytest.fixture
def mock_tools():
    return [
        Tool(
            name="search",
            description="Search for items",
            inputSchema={
                "type": "object",
                "properties": {"query": {"type": "string"}},
                "required": ["query"]
            }
        )
    ]

@pytest.fixture
def mock_session(mock_tools):
    session = AsyncMock()
    session.list_tools.return_value = mock_tools
    session.call_tool.return_value = CallToolResult(
        content=[TextContent(type="text", text="result")],
        isError=False
    )
    session.is_connected = True
    return session

@pytest.fixture
def mock_client(mock_session):
    client = MagicMock()
    client.create_all_sessions = AsyncMock()
    client.get_session = MagicMock(return_value=mock_session)
    client.close_all_sessions = AsyncMock()
    return client

Verifying Tool Discovery

@pytest.mark.asyncio
async def test_tool_discovery(mock_client, mock_session, mock_tools):
    await mock_client.create_all_sessions()
    session = mock_client.get_session("test-server")
    tools = await session.list_tools()

    assert len(tools) == len(mock_tools)
    assert tools[0].name == "search"
    assert "query" in tools[0].inputSchema["properties"]
    mock_session.list_tools.assert_awaited_once()

Asserting a Tool Was Actually Called

@pytest.mark.asyncio
async def test_tool_execution(mock_client, mock_session):
    await mock_client.create_all_sessions()
    session = mock_client.get_session("test-server")
    result = await session.call_tool("search", {"query": "test"})

    mock_session.call_tool.assert_awaited_once_with("search", {"query": "test"})
    assert result.content[0].text == "result"
    assert not result.isError

Testing the Full Agent Loop

@pytest.mark.asyncio
async def test_agent_run():
    with patch("mcp_use.MCPClient") as MockClient:
        mock_client = MagicMock()
        MockClient.return_value = mock_client
        mock_client.create_all_sessions = AsyncMock()
        mock_client.close_all_sessions = AsyncMock()

        # Mock the session and tools
        mock_session = AsyncMock()
        mock_session.list_tools.return_value = [
            Tool(name="add", description="Add numbers",
                 inputSchema={"type": "object", "properties": {"a": {"type": "number"}, "b": {"type": "number"}}})
        ]
        mock_client.get_session.return_value = mock_session

        # The agent run would be tested via integration test with a real LLM
        # or by mocking the LangChain agent executor

Async Test Setup with pytest-asyncio

# conftest.py
import pytest

@pytest.fixture(scope="session")
def event_loop_policy():
    """Use default event loop policy for all tests."""
    return None

# In pyproject.toml or pytest.ini:
# [tool.pytest.ini_options]
# asyncio_mode = "auto"  # All async tests run automatically

Common Failure Signatures

Error Message	Derailment	Check
`ModuleNotFoundError: No module named 'mcp.server'` in a consumer file	Pattern 1	Verify imports use `mcp_use`, not `mcp.server`
`AttributeError: 'MCPClient' object has no attribute 'tool'`	Pattern 2	MCPClient discovers tools, doesn't define them
`KeyError: 'parameters'` when accessing tool schema	Pattern 3	MCP uses `inputSchema`, not `parameters`
`AttributeError: 'NoneType' object has no attribute 'list_tools'`	Pattern 4	Call `create_session()` before `get_session()`
`RuntimeError: no running event loop`	Pattern 4	Wrap in `async def` + `asyncio.run()`
`TypeError: object NoneType can't be used in 'await' expression`	Pattern 4	Missing `await` on async call
`Error code: 400 - Invalid 'messages[N].tool_calls[0].function.name': string does not match pattern '^[a-zA-Z0-9_-]+$'`	Pattern 5	Tool name contains dots; sanitize or use different LLM
`ToolException: tool-name is not a valid tool`	Pattern 5	Check tool name matches `list_tools()` output exactly
`ModuleNotFoundError: No module named 'langchain.llms'`	Pattern 6	Use `langchain_openai`, not `langchain.llms`
`ImportError: cannot import name 'initialize_agent'`	Pattern 6	Removed in LangChain 1.0; use `MCPAgent` instead
`ModuleNotFoundError: No module named 'langchain_openai'`	Pattern 6	Run `pip install langchain-openai`
`ValueError: Unrecognized message part type: thinking`	N/A (Gemini)	Known Gemini issue (#110); filter thinking blocks or use different model
`RuntimeError: Code mode is not enabled`	N/A (Config)	Set `code_mode=True` in `MCPClient` constructor

Migrating to mcp-use

This section maps official @modelcontextprotocol/sdk (TypeScript) patterns to their mcp-use equivalents. If an AI agent sees official SDK patterns in existing code and needs to understand the mcp-use way, use this mapping.

Server Creation

Official TS SDK:

import { McpServer } from '@modelcontextprotocol/server';
import { StdioServerTransport } from '@modelcontextprotocol/server';

const server = new McpServer(
    { name: 'my-server', version: '1.0.0' },
    { capabilities: { tools: {}, resources: { listChanged: true } } }
);

const transport = new StdioServerTransport();
await server.connect(transport);

mcp-use TS equivalent:

import { MCPServer } from 'mcp-use/server'

const server = new MCPServer({
    name: 'my-server',
    version: '1.0.0',
})

await server.listen(3000)  // Built-in HTTP + transport handling

mcp-use Python equivalent:

from mcp_use import MCPServer

server = MCPServer(name="my-server")
# Tools registered via decorators, then:
# server.run() or use with uvicorn

Key differences:

mcp-use wraps the official SDK internally — no need to import both
Transport is automatic (stdio for CLI, Streamable HTTP for listen())
No manual connect(transport) needed — listen() handles everything
Session management, CORS, and base path are built-in config options

Tool Definition

Official TS SDK:

server.registerTool('calculate-bmi', {
    title: 'BMI Calculator',
    description: 'Calculate BMI',
    inputSchema: z.object({
        weightKg: z.number(),
        heightM: z.number()
    }),
    outputSchema: z.object({ bmi: z.number() }),
}, async ({ weightKg, heightM }) => ({
    content: [{ type: 'text', text: String(weightKg / (heightM * heightM)) }],
    structuredContent: { bmi: weightKg / (heightM * heightM) }
}));

mcp-use TS equivalent:

import { text } from 'mcp-use/server'

server.tool({
    name: 'calculate-bmi',
    description: 'Calculate BMI',
    schema: z.object({
        weightKg: z.number(),
        heightM: z.number()
    }),
}, async ({ weightKg, heightM }) => {
    return text(`BMI: ${weightKg / (heightM * heightM)}`)
})

mcp-use Python equivalent:

@server.tool(name="calculate_bmi", description="Calculate BMI")
async def calculate_bmi(
    weight_kg: Annotated[float, Field(description="Weight in kg")],
    height_m: Annotated[float, Field(description="Height in m")],
) -> str:
    return f"BMI: {weight_kg / (height_m ** 2)}"

Key differences:

registerTool() → server.tool() (config object + callback)
inputSchema → schema (same Zod, different key name)
Manual content: [{ type: 'text', text: '...' }] → text() helper
Response helpers: text(), object(), markdown(), image(), audio(), binary(), error(), mix()

Resource Definition

Official TS SDK:

import { ResourceTemplate } from '@modelcontextprotocol/server';

server.registerResource('user', new ResourceTemplate('users://{id}', {
    list: async () => ({ resources: [{ uri: 'users://1', name: 'Alice' }] })
}), { title: 'User Profile' }, async (uri, { id }) => ({
    contents: [{ uri: uri.href, text: JSON.stringify({ id, name: `User ${id}` }) }]
}));

mcp-use TS equivalent:

server.resourceTemplate({
    uriTemplate: 'users://{id}',
    name: 'User Profile',
    mimeType: 'application/json',
}, async ({ id }) => object({ id, name: `User ${id}` }))

mcp-use Python equivalent:

@server.resource(uri="users://{user_id}", name="user_profile", mime_type="application/json")
async def user_profile(user_id: str) -> str:
    return json.dumps({"id": user_id, "name": f"User {user_id}"})

Prompt Definition

Official TS SDK:

server.registerPrompt('review-code', {
    title: 'Code Review',
    argsSchema: z.object({ code: z.string() })
}, ({ code }) => ({
    messages: [{ role: 'user', content: { type: 'text', text: `Review:\n${code}` } }]
}));

mcp-use TS equivalent:

server.prompt({
    name: 'review-code',
    description: 'Code review prompt',
    schema: z.object({ code: z.string() }),
}, async ({ code }) => text(`Review:\n${code}`))

mcp-use Python equivalent:

@server.prompt(name="review_code", title="Code Review")
def review_code(code: Annotated[str, Field(description="Code to review")]) -> str:
    return f"Review:\n{code}"

Transport Setup

Official TS SDK:

// Stdio
const transport = new StdioServerTransport();
await server.connect(transport);

// HTTP (manual setup required)
import express from 'express';
const app = express();
const transport = new StreamableHTTPServerTransport({ sessionIdGenerator: () => randomUUID() });
app.post('/mcp', async (req, res) => { await transport.handleRequest(req, res, req.body); });
app.get('/mcp', async (req, res) => { /* SSE handler */ });
app.listen(3000);

mcp-use equivalent:

// HTTP (one-liner)
await server.listen(3000)  // Handles /mcp endpoint, SSE, sessions automatically

// CLI workflow
// mcp-use dev
// mcp-use build
// mcp-use start

Session Management

Official TS SDK: Manual — you track transports in a Map, route by session ID header.

mcp-use: Built-in pluggable storage:

import { RedisSessionStore, RedisStreamManager } from 'mcp-use/server'

const server = new MCPServer({
    name: 'my-server',
    sessionStore: new RedisSessionStore({ client: redis }),
    streamManager: new RedisStreamManager({ client: redis, pubSubClient: pubSubRedis }),
})

Storage backends: FileSystemSessionStore (development default), InMemorySessionStore (production default without custom store), RedisSessionStore (distributed production).

Authentication

Official TS SDK: Manual middleware — implement OAuthServerProvider, wire up auth endpoints yourself.

mcp-use: Built-in providers:

import { MCPServer, oauthAuth0Provider } from 'mcp-use/server'

const server = new MCPServer({
    name: 'protected-server',
    oauth: oauthAuth0Provider({
        domain: 'your-tenant.auth0.com',
        audience: 'https://your-api.example.com',
    }),
})

Providers: oauthAuth0Provider, oauthSupabaseProvider, oauthWorkOSProvider, oauthKeycloakProvider, oauthCustomProvider.

Quick Migration Checklist

Official SDK Pattern	mcp-use Equivalent	Notes
`new McpServer(info, options)`	`new MCPServer(config)`	Config includes transport, sessions, OAuth
`server.registerTool(name, config, cb)`	`server.tool(config, cb)`	`inputSchema` → `schema`
`server.registerResource(name, uri, meta, cb)`	`server.resource(config, cb)`	Simpler signature
`server.registerPrompt(name, config, cb)`	`server.prompt(config, cb)`	Response helpers work
`new StdioServerTransport()` + `server.connect(t)`	`server.listen()` or `mcp-use dev/start` workflow	Built-in HTTP transport/session handling
`new StreamableHTTPServerTransport(opts)`	`server.listen(port)`	Built-in HTTP server
Manual session Map + routing	`sessionStore: new RedisSessionStore(...)`	Pluggable backends
Manual OAuth middleware	`oauth: oauthAuth0Provider(...)`	5 built-in providers
Manual `content: [{ type: 'text', text }]`	`text(string)`	10+ response helpers
`ctx.mcpReq.log('info', msg)`	`ctx.log('info', msg)`	Simplified logging

mcp-use-code-review

Test MCP-Use SDK Based Apps

What mcp-use IS vs. What It Is NOT

Server Config Schema

Stdio (command-based)

HTTP / SSE / Streamable HTTP

WebSocket

Loading the config

Correct Client Lifecycle

High-level (MCPAgent — most common)

Low-level (MCPClient direct usage)

MCPSession as context manager

What requires async/await

6 AI Derailment Patterns

Pattern 1: Server SDK vs. Client SDK Conflation

Pattern 2: Claude Agent SDK @tool Decorator Misapplication

Pattern 3: Tool Schema Field Name Mismatch

Pattern 4: Missing Async Lifecycle Steps

Pattern 5: Tool Name Format Incompatibility

Pattern 6: LangChain Import Path / Version Mismatch

Review Checklist

Import Correctness

Config Correctness

Async Correctness

Lifecycle Correctness

Tool Usage

Test Patterns

Mocking an MCP Server for Unit Tests

Verifying Tool Discovery

Asserting a Tool Was Actually Called

Testing the Full Agent Loop

Async Test Setup with pytest-asyncio

Common Failure Signatures

Migrating to mcp-use

Server Creation

Tool Definition

Resource Definition

Prompt Definition

Transport Setup

Session Management

Authentication

Quick Migration Checklist