FastMCP

Name: FastMCP
Author: jlowin

BLOCKgrade F · trust 27/100

🚀 The fast, Pythonic way to build MCP servers and clients.

agentsfastmcpllmsmcpmcp clientsmcp serversmcp toolsmodel context protocol

Overview

From the repository's own README, as read at the audited commit.

<div align="center"><!-- omit in toc --><picture>  <source width="550" media="(prefers-color-scheme: dark)" srcset="https://raw.githubusercontent.com/PrefectHQ/fastmcp/main/docs/assets/brand/f-watercolor-waves-4-dark.png">  <source width="550" media="(prefers-color-scheme: light)" srcset="https://raw.githubusercontent.com/PrefectHQ/fastmcp/main/docs/assets/brand/f-watercolor-waves-4.png">  <img width="550" alt="FastMCP Logo" src="https://raw.githubusercontent.com/PrefectHQ/fastmcp/main/docs/assets/brand/f-watercolor-waves-2.png"></picture># FastMCP 🚀<strong>Move fast and make things.</strong>*Made with 💙 by [Prefect](https://www.prefect.io/)*[![Docs](https://img.shields.io/badge/docs-gofastmcp.com-blue)](https://gofastmcp.com)[![Discord](https://img.shields.io/badge/community-discord-5865F2?logo=discord&logoColor=white)](https://discord.gg/uu8dJCgttd)[![PyPI - Version](https://img.shields.io/pypi/v/fastmcp.svg)](https://pypi.org/project/fastmcp)[![TypeScript](https://img.shields.io/npm/v/%40prefecthq%2Ffastmcp-ts?label=typescript&color=3178c6)](https://github.com/PrefectHQ/fastmcp-ts)[![Tests](https://github.com/PrefectHQ/fastmcp/actions/workflows/run-tests.yml/badge.svg)](https://github.com/PrefectHQ/fastmcp/actions/workflows/run-tests.yml)[![License](https://img.shields.io/github/license/PrefectHQ/fastmcp.svg)](https://github.com/PrefectHQ/fastmcp/blob/main/LICENSE)<a href="https://trendshift.io/repositories/21461" target="_blank"><img src="https://trendshift.io/api/badge/repositories/21461" alt="prefecthq%2Ffastmcp | Trendshift" style="width: 250px; height: 55px;" width="250" height="55"/></a></div>---The [Model Context Protocol](https://modelcontextprotocol.io/) (MCP) connects LLMs to tools and data. FastMCP is a full MCP application framework for servers, clients, and interactive apps. A server starts with ordinary Python:```pythonfrom fastmcp import FastMCPmcp = FastMCP("Demo 🚀")@mcp.tooldef add(a: int, b: int) -> int:    """Add two numbers"""    return a + bi

Connect

Built from this server's own package name, version and transport as found in its source — not copied from anyone's documentation, so it cannot drift against a page we do not control. Replace the environment placeholders with a token scoped to the least it needs.

claude-code

claude mcp add fastmcp --env AUTH0_CONFIG_URL=${AUTH0_CONFIG_URL} --env AUTHKIT_DOMAIN=${AUTHKIT_DOMAIN} --env FASTMCP_GITHUB_TOKEN=${FASTMCP_GITHUB_TOKEN} --env FASTMCP_SERVER_AUTH_AWS_COGNITO_AWS_REGION=${FASTMCP_SERVER_AUTH_AWS_COGNITO_AWS_REGION} -- uvx fastmcp

claude-desktop

{
  "mcpServers": {
    "fastmcp": {
      "command": "uvx",
      "args": [
        "fastmcp"
      ],
      "env": {
        "AUTH0_CONFIG_URL": "${AUTH0_CONFIG_URL}",
        "AUTHKIT_DOMAIN": "${AUTHKIT_DOMAIN}",
        "FASTMCP_GITHUB_TOKEN": "${FASTMCP_GITHUB_TOKEN}",
        "FASTMCP_SERVER_AUTH_AWS_COGNITO_AWS_REGION": "${FASTMCP_SERVER_AUTH_AWS_COGNITO_AWS_REGION}"
      }
    }
  }
}

Exposed tools (200) 265 read · 37 write · 3 destructive

Blast radius: 3 tools can delete or overwrite. An agent that can be talked into calling a tool can be talked into calling this one.

Tool	Risk	Description
`_trigger_docket`	write	return
`add`	write	return a + b
`add_comment`	write	Add a comment to a request. Returns the updated request.
`add_item`	write	Add a new item to inventory and return the full list.
`add_numbers`	write	Add two numbers
`admin_tool`	read	return
`analyze_data`	read	Filter and analyze sales data. Returns rows, summary, and chart data.
`analyze_portfolio`	read	Analyze a portfolio of stock symbols.
`annotate`	read	current = trace.get_current_span()
`api_health`	read	Show health details for each API endpoint.
`approve_request`	read	Approve a pending request and return updated lists.
`ask_name`	read	result = await ctx.elicit(
`async_echo`	read	Async tool for testing
`async_tool`	read	An async tool.
`background_tool`	read	return x
`bare_sync_access`	write	headers = get_http_headers()
`bare_tool`	read	info = get_task_context()
`batch_process`	read	Process batches.
`bg_progress_tool`	read	await progress.set_total(3)
`bg_tool`	read	await asyncio.sleep(0.01)
`blocked`	read	return
`blocking`	write	import time
`book_flight`	read	return _ask(
`boom`	read	raise ValueError(
`calc`	read	return
`calculate`	write	Add two numbers (v1.0).
`call_api`	read	return f
`capture_docket_id`	read	docket_ids.append((call_num, id(docket)))
`charge`	read	Charge a payment (v1.0 - basic).
`check_both`	read	assert isinstance(docket, Docket)
`check_docket`	read	assert isinstance(docket, Docket)
`check_headers`	read	headers = _worker_snapshot_headers()
`check_permission`	read	return f
`check_request_header`	read	return _worker_snapshot_headers().get(
`check_token`	read	token = get_access_token()
`check_worker_status`	read	return f
`checkpoint`	read	if ctx.request_state is None:
`claimed_tool`	read	return None
`combine`	read	return f
`compute`	read	Compute something.
`confirm_delete`	destructive	Parks the task on one elicitation before doing the (pretend) deletion.
`contact_form`	write	Show a form to create a new contact, with a live contact list below.
`context_sync_access`	write	headers = get_http_headers()
`coordinated`	write	started.set()
`count`	read	return 1
`create`	write	Create item
`create_project`	write	return
`create_user`	write	Create a user.
`crunch`	read	...
`custom`	read	A custom tool
`custom-add`	write	return x + y
`custom_name`	read	return str(x)
`custom_save`	write	return name
`custom_tool`	read	A custom tool
`declared_status`	read	return {
`delete_item`	destructive	Remove an item by ID and return the remaining inventory.
`demo`	read	A demo app that exercises various MCP message types.
`double`	read	return n * 2
`dynamic_add`	write	Add two numbers with offset
`dynamic_multiply`	read	Multiply two numbers
`echo`	read	Echo a message back.
`echo_with_logs`	read	Echo a message and emit log notifications.
`employee_directory`	read	Show a searchable, sortable employee directory.
`enabled`	read	Task enabled
`enter_env`	read	await ctx.disable_components(tags={
`error_tool`	read	raise ToolError(
`excluded_versioned_tool`	read	return
`execute_trade`	write	Execute a trade (simulated).
`exit_env`	read	await ctx.reset_visibility()
`explicit_tool`	read	return {
`explodes`	read	raise MCPError(code=INTERNAL_ERROR, message=
`f`	read	return 42
`fail`	read	Always raises an error.
`failing_tool`	read	raise ValueError(
`farewell`	read	Say farewell in their language.
`fast_async_tool`	read	await anyio.sleep(0.01)
`fast_sync_tool`	write	time.sleep(0.01)
`fast_tool`	read	return x * 2
`feature_flags`	read	Toggle feature flags with live preview.
`fetch`	read	Fetch data from
`fetch_data`	read	return (
`filter_by_category`	read	Filter inventory by category. Pass
`filter_data`	read	Filter sales data by region and/or product.
`finance_tool`	read	return
`forbidden`	read	Forbidden tool
`forever`	read	await asyncio.Event().wait()
`full_name`	read	responses = ctx.input_responses
`get_auth_type`	read	auth = headers.get(
`get_client_ip`	read	return request.client.host if request.client else
`get_market_data`	read	Get current market data for a symbol.
`get_my_emails`	read	async with httpx2.AsyncClient() as client:
`get_node`	read	Get a node
`get_pr`	read	Get a pull request
`get_request_details`	read	Get full details for a single request. Available to both model and UI.
`get_request_id`	read	return ctx.request_id
`get_summary`	read	Return summary statistics for the full dataset.
`get_test_file_from_server`	read
`get_test_pdf_from_url`	read
`get_user_id`	read	return token.claims.get(
`get_weather`	read	Get the current weather
`greet`	read	Greet someone in their language.
`greet_user`	read	return f
`guard`	read	calls.append(1)
`hidden_tool`	read	return
`included_versioned_tool`	read	return
`info`	read	return
`inspect_items`	read	return {
`instant_timeout`	read	await anyio.sleep(0) # Give the event loop a chance to check timeout
`internal_tool`	read	return
`introspect`	read	return f
`leak`	read	raise ValueError(
`list_contacts`	read	Return all contacts. Visible to both the model and the UI.
`list_requests`	read	List requests, optionally filtered by status.
`list_users`	read	List all system users.
`log_progress`	read	ctx.report_progress(50, 100,
`long_timeout`	read	await anyio.sleep(0.01)
`make_tool`	read	return
`mixed_audio_list_fn`	read	return [
`mixed_deps`	read	assert isinstance(ctx, Context)
`mixed_file_list_fn`	read	return [
`mixed_list_fn`	read	return [
`modify`	write	Modify the data provided.
`multi_input`	read	Parks the task on two elicitations at once, so they can be answered separately.
`multiply`	read	return x * y
`my_function`	read	return f
`my_task`	read	# Works transparently in both foreground and background task modes
`my_tool`	read	A tool
`mytool`	read	return
`new_tool`	read	return
`no_task_tool`	read	return
`normal_tool`	read	return config[
`ok`	read	return
`old_tool`	read	return
`one`	read	return 1
`one_question`	read	responses = ctx.input_responses
`only_v5`	read	return
`pick`	read	return
`ping`	read	Ping the server
`plan_dinner`	read	Plan a dinner menu, asking the user what they
`positional_name`	read
`premium_tool`	read	return
`private_tool`	read	return f
`process_data`	read	return f
`progress_tool`	read	await ctx.report_progress(0, 100,
`project_overview`	read	Show project details organized in tabs.
`protected`	read	return
`protocol_error_job`	read	Raises a protocol-level error: `failed` with an inlined `error`.
`quarterly_revenue`	read	Show quarterly revenue as a bar chart.
`query`	read	return []
`query_data`	read	assert connection.is_open
`query_db`	read	return f
`query_sync`	write	assert connection.is_open
`quick_task`	read	return value * 2
`quick_tool`	read	return value * 2
`read_it`	read	val = await ctx.get_state(
`refresh`	read	Collect fresh system stats.
`regular_tool`	read	return
`reject_request`	read	Reject a pending request and return updated lists.
`remember`	read	facts = await session.get(
`remote_task_tool`	read	A remote tool that supports tasks
`report`	read	return note
`reset_user_password`	destructive	Reset a user
`return_audio`	read	return Audio(path=str(test_audio))
`return_bool`	read	return True
`return_bytes`	read	return b
`return_dataclass`	read	return PersonDataclass(name=
`return_datetime`	read	return datetime(2025, 11, 5, 12, 30, 45)
`return_dict`	read	return {
`return_embedded_resource`	read	return EmbeddedResource(
`return_empty_dict`	read	return {}
`return_empty_list`	read	return []
`return_file`	read	return File(path=str(test_file))
`return_float`	read	return 3.14159
`return_image_content`	read	return ImageContent(
`return_image_data`	read	return Image(data=test_image.read_bytes(), format=
`return_image_path`	read	return Image(path=str(test_image))
`return_int`	read	return 42
`return_list`	read	return [
`return_mixed_content`	read	return [
`return_model`	read	return UserData(name=
`return_none`	read	return None
`return_optional`	read	return
`return_optional_none`	read	return None
`return_path`	read	return Path(
`return_resource_link`	read	return ResourceLink(
`return_set`	write	return {1, 2, 3}
`return_string`	read	return
`return_text_content`	read	return TextContent(type=
`return_tuple`	read	return (42,
`return_typeddict`	read	return {
`return_union`	read	return
`return_union_int`	read	return 123
`return_uuid`	read	return UUID(
`run`	write	Run something
`run_query`	write	...
`sales_chart`	read	Show monthly online vs. retail sales as a bar chart.
`sales_dashboard`	read	Company sales dashboard with KPIs, revenue trends, segment breakdown, and recent deals.
`sample_tool`	read	return x * 2
`save`	write	return f
`save_contact`	write	Save a new contact and return the updated list.

Details

Source: jlowin/fastmcp
PyPI: fastmcp
Transports: sse · stdio · streamable-http
Credentials it reads: AUTH0_CONFIG_URLAUTHKIT_DOMAINFASTMCP_GITHUB_TOKENFASTMCP_SERVER_AUTH_AWS_COGNITO_AWS_REGIONFASTMCP_SERVER_AUTH_AWS_COGNITO_CLIENT_IDFASTMCP_SERVER_AUTH_AWS_COGNITO_CLIENT_SECRETFASTMCP_SERVER_AUTH_AWS_COGNITO_USER_POOL_IDFASTMCP_SERVER_AUTH_AZURE_CLIENT_IDFASTMCP_SERVER_AUTH_AZURE_CLIENT_SECRETFASTMCP_SERVER_AUTH_AZURE_TENANT_IDFASTMCP_SERVER_AUTH_CLERK_CLIENT_IDFASTMCP_SERVER_AUTH_CLERK_CLIENT_SECRET
License: Apache-2.0
Stars: 27,717 · pushed 0d ago

Trust audit

Do not install this without reading the findings. The audit found something that could harm you or your machine.

Layer	What it checks	Result
L0	Provenance & inventory	WARN
L1	Static analysis of the code	FAIL
L2	Instruction surface (what it tells the agent)	FAIL
L3	Class-specific surface	WARN
L4	Behavioural (sandbox)	SKIPPED

What the source does

Filesystem: declared (4 observation(s))
Network: declared (2 observation(s))
Shell: declared (5 observation(s))
Dependencies: not all pinned
Secrets in source: found

Findings (25)

HIGHCode injection · code.deserialize · CWE-78, CWE-94, CWE-95

fastmcp_slim/fastmcp/server/providers/skills/_common.py:105

parsed = yaml.load(frontmatter_text, Loader=yaml.BaseLoader)

Why it matters. deserialises untrusted bytes into live objects

Fix. use json or yaml.safe_load

HIGHPrompt injection · prompt.hide_from_user · CWE-94, CWE-1427

docs/getting-started/upgrading/from-mcp-sdk-v2.mdx:87

FastMCP has no resolver injection, but the underlying requests survive in a different shape: on a modern connection `Elicit`, `Sample`, and `ListRoots` all ride the guard pattern, where the tool retur

Why it matters. asks the agent to act without the user's knowledge

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/code-review

.claude/skills/code-review

Why it matters. link not followed

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/fix-issue

.claude/skills/fix-issue

Why it matters. link not followed

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/python-tests

.claude/skills/python-tests

Why it matters. link not followed

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/release

.claude/skills/release

Why it matters. link not followed

MEDIUMInventory / provenance · inv.symlink · CWE-1104

.claude/skills/review-issue

.claude/skills/review-issue

Why it matters. link not followed

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

fastmcp_slim/fastmcp/server/__init__.py:14

return importlib.import_module(f"fastmcp.server.{name}")

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

fastmcp_slim/fastmcp/server/providers/filesystem_discovery.py:197

return importlib.import_module(private_name)

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

fastmcp_slim/fastmcp/server/providers/filesystem_discovery.py:213

return importlib.import_module(module_name)

MEDIUMCode injection · code.dynamic_import · CWE-78, CWE-94, CWE-95

fastmcp_slim/fastmcp/utilities/mcp_server_config/v1/sources/filesystem.py:132

server_module = importlib.import_module(module_name)

MEDIUMHard-coded secrets · secret.db_uri · CWE-798, CWE-321

examples/memory.py:40

DB_DSN = "postgresql://postgres:postgres@localhost:54320/memory_db"

MEDIUMHard-coded secrets · secret.db_uri · CWE-798, CWE-321

examples/memory.py:302

"postgresql://postgres:postgres@localhost:54320/postgres"

MEDIUMHard-coded secrets · secret.generic · CWE-798, CWE-321

tests/server/http/test_stale_access_token.py:60

token="stale-token-from-initial-auth",

MEDIUMHard-coded secrets · secret.generic · CWE-798, CWE-321

tests/server/http/test_stale_access_token.py:68

token="fresh-token-after-refresh",

MEDIUMHard-coded secrets · secret.generic · CWE-798, CWE-321

tests/server/http/test_stale_access_token.py:206

token="sdk-token-no-subject",

MEDIUMHard-coded secrets · secret.private_key · CWE-798, CWE-321

tests/server/auth/test_jwt_provider.py:208

assert "-----BEGIN PRIVATE KEY-----" in private_pem

MEDIUMFilesystem / path · mcp.destructive_tools · CWE-22, CWE-59

confirm_delete, delete_item, reset_user_password

Why it matters. 3 tool(s) can delete or overwrite

Fix. prefer a read-only mode or scoped tokens; the page states the blast radius