Simple HTTP MCP Server
This server acts as a lightweight HTTP/STDIO gateway that exposes Python functions as discoverable and executable tools under the Model Context Protocol (MCP). It enables remote tool execution via JSON-RPC interface with both stateful and stateless contexts.
Key Capabilities:
Remote Tool Execution: Execute Python functions remotely through HTTP POST requests or STDIO
Tool Discovery: Discover available tools and their specifications via the MCP protocol
Dual Context Support: Maintain state across tool calls (stateful) or access incoming request data like headers and cookies (stateless)
Type-Safe Validation: Uses Pydantic for robust input/output schema validation and serialization
Asynchronous Handling: Provides async request processing via Starlette or FastAPI
Example Tools:
get_weather: Retrieve weather data for specified locations with temperature unit optionsget_time: Fetch current timetool_that_access_request: Access request details like username from headersget_called_tools: Retrieve list of previously called tools using stateful context
Provides a framework for building HTTP-based MCP servers that can be integrated into FastAPI applications, enabling the exposure of Python functions as discoverable tools and prompts
Uses Pydantic models for type-safe data validation and serialization of tool inputs, outputs, and server configurations
Click on "Install Server".
Wait a few minutes for the server to deploy. Once ready, it will show a "Started" state.
In the chat, type
@followed by the MCP server name and your instructions, e.g., "@Simple HTTP MCP Servergreet me with 'Hello, how can I help you today?'"
That's it! The server will respond to your query, and you can continue using it as needed.
Here is a step-by-step guide with screenshots.
Simple HTTP MCP Server Implementation
This project provides a lightweight server implementation for the Model Context Protocol (MCP) over HTTP. It allows you to expose Python functions as tools and prompts that can be discovered and executed remotely via a JSON-RPC interface. It is intended to be used with a Starlette or FastAPI application (see demo).
Table of Contents
Related MCP server: Python REPL MCP Server
Features
MCP Protocol Compliant: Implements the MCP specification for tool and prompts discovery and execution. No support for notifications.
HTTP and STDIO Transport: Uses HTTP (POST requests) or STDIO for communication.
Async Support: Built on
StarletteorFastAPIfor asynchronous request handling.Type-Safe: Leverages
Pydanticfor robust data validation and serialization.Server State Management: Access shared state through the lifespan context using the
get_state_keymethod.Request Access: Access the incoming request object from your tools and prompts.
Authorization Scopes: Support for scope-based authorization using Starlette's authentication system.
Error Handling: Tools can optionally return error messages instead of raising exceptions.
OAuth 2.1 Authorization: Optional
auth_mcppackage with Bearer token validation, Protected Resource Metadata (RFC 9728), andWWW-Authenticateerror responses. Install withpip install http-mcp[auth].
Server Architecture
The library provides a single MCPServer class that uses lifespan to manage
shared state across the entire application lifecycle.
MCPServer
The MCPServer is designed to work with Starlette's lifespan system for
managing shared server state.
Key Characteristics:
Lifespan Based: Uses Starlette's lifespan events to initialize and manage shared server state
Application-Level State: State persists across the entire application lifecycle, not per-request
Flexible: Can be used with any custom context class stored in the lifespan state
Constructor Parameters:
name(str): The name of your MCP serverversion(str): The version of your MCP servertools(tuple[Tool, ...]): Tuple of tools to expose (default: empty tuple)prompts(tuple[Prompt, ...]): Tuple of prompts to expose (default: empty tuple)instructions(str | None): Optional instructions for AI assistants on how to use this server
Example Usage:
import contextlib
from collections.abc import AsyncIterator
from typing import TypedDict
from dataclasses import dataclass, field
from starlette.applications import Starlette
from http_mcp.server import MCPServer
@dataclass
class Context:
call_count: int = 0
user_preferences: dict = field(default_factory=dict)
class State(TypedDict):
context: Context
@contextlib.asynccontextmanager
async def lifespan(_app: Starlette) -> AsyncIterator[State]:
yield {"context": Context()}
mcp_server = MCPServer(
name="my-server",
version="1.0.0",
tools=my_tools,
prompts=my_prompts,
instructions="Optional instructions for AI assistants on how to use this server"
)
app = Starlette(lifespan=lifespan)
app.mount("/mcp", mcp_server.app)Tools
Tools are the functions that can be called by the client.
Basic Tool Example
Define the arguments and output for the tools:
# app/tools/models.py
from pydantic import BaseModel, Field
class GreetInput(BaseModel):
question: str = Field(description="The question to answer")
class GreetOutput(BaseModel):
answer: str = Field(description="The answer to the question")
# Note: the description on Field will be passed when listing the tools.
# Having a description is optional, but it's recommended to provide one.Define the tools:
# app/tools/tools.py
from http_mcp.types import Arguments
from app.tools.models import GreetInput, GreetOutput
def greet(args: Arguments[GreetInput]) -> GreetOutput:
return GreetOutput(answer=f"Hello, {args.inputs.question}!")
# app/tools/__init__.py
from http_mcp.types import Tool
from app.tools.models import GreetInput, GreetOutput
from app.tools.tools import greet
TOOLS = (
Tool(
func=greet,
inputs=GreetInput,
output=GreetOutput,
),
)
__all__ = ["TOOLS"]
Instantiate the server:
# app/main.py
from starlette.applications import Starlette
from http_mcp.server import MCPServer
from app.tools import TOOLS
mcp_server = MCPServer(tools=TOOLS, name="test", version="1.0.0")
app = Starlette()
app.mount(
"/mcp",
mcp_server.app,
)Tools Without Arguments
You can define tools that don't require any input arguments:
from datetime import UTC, datetime
from pydantic import BaseModel, Field
from http_mcp.types import Tool
class GetTimeOutput(BaseModel):
time: str = Field(description="The current time")
async def get_time() -> GetTimeOutput:
"""Get the current time."""
return GetTimeOutput(time=datetime.now(UTC).strftime("%H:%M:%S"))
TOOLS = (
Tool(
func=get_time,
inputs=type(None), # No arguments required
output=GetTimeOutput,
),
)Alternatively, you can use the NoArguments class for better clarity:
from http_mcp.types import Arguments, NoArguments, Tool
class SimpleOutput(BaseModel):
success: bool = Field(description="Whether the operation was successful")
def simple_tool(args: Arguments[NoArguments]) -> SimpleOutput:
"""A simple tool with no arguments."""
# You can still access request and state
context = args.get_state_key("context", Context)
return SimpleOutput(success=True)
TOOLS = (
Tool(
func=simple_tool,
inputs=NoArguments,
output=SimpleOutput,
),
)Tools with Error Handling
Tools can optionally return error messages instead of raising exceptions:
from pydantic import BaseModel, Field
from http_mcp.types import Arguments, Tool
from http_mcp.exceptions import ToolInvocationError
class RiskyToolInput(BaseModel):
value: int = Field(description="An integer value")
class RiskyToolOutput(BaseModel):
result: str = Field(description="The result of the operation")
def risky_tool(args: Arguments[RiskyToolInput]) -> RiskyToolOutput:
"""A tool that might fail."""
if args.inputs.value < 0:
raise ToolInvocationError("risky_tool", "Value must be positive")
return RiskyToolOutput(result=f"Success: {args.inputs.value}")
TOOLS = (
Tool(
func=risky_tool,
inputs=RiskyToolInput,
output=RiskyToolOutput,
return_error_message=True, # Return ErrorMessage instead of raising
),
)When return_error_message=True, the tool will return an ErrorMessage model
with the error details instead of raising a ToolInvocationError.
Tools with Authorization Scopes
You can restrict tool access based on authentication scopes:
from http_mcp.exceptions import ToolInvocationError
from http_mcp.types import Arguments, NoArguments, Tool
from starlette.authentication import has_required_scope
class SecureOutput(BaseModel):
message: str = Field(description="A secure message")
def private_tool(args: Arguments[NoArguments]) -> SecureOutput:
"""A tool that requires authentication."""
if not has_required_scope(args.request, ("private",)):
raise ToolInvocationError("private_tool", "Insufficient scope")
return SecureOutput(message="This is private data")
def admin_tool(args: Arguments[NoArguments]) -> SecureOutput:
"""A tool that requires admin or superuser scope."""
if not has_required_scope(args.request, ("admin", "superuser")):
raise ToolInvocationError("admin_tool", "Insufficient scope")
return SecureOutput(message="This is admin data")
TOOLS = (
Tool(
func=private_tool,
inputs=NoArguments,
output=SecureOutput,
scopes=("private",), # Only accessible with 'private' scope
),
Tool(
func=admin_tool,
inputs=NoArguments,
output=SecureOutput,
scopes=("admin", "superuser"), # Accessible with either scope
),
)Note: You need to set up authentication middleware in your Starlette app for
scopes to work properly. The scopes field on Tool is the primary
authorization gate — the framework filters tools by scope before invocation. The
raise ToolInvocationError(...) calls inside the tool functions above are
optional defense-in-depth checks that return a proper error response to the
client instead of silently failing.
Server State Management
The server uses Starlette's lifespan system to manage shared state across the
entire application lifecycle. State is initialized when the application starts
and persists until it shuts down. Context is accessed through the
get_state_key method on the Arguments object.
This is useful for sharing resources like database connection pools, HTTP clients, caches, or any application state across tools.
Database Connection Pool
The most common pattern — initialize a connection pool at startup, share it across all tools, and close it on shutdown:
# app/context.py
from dataclasses import dataclass
import asyncpg
@dataclass
class AppContext:
db: asyncpg.Pool# app/main.py
import contextlib
import os
from collections.abc import AsyncIterator
from typing import TypedDict
import asyncpg
from starlette.applications import Starlette
from http_mcp.server import MCPServer
from app.context import AppContext
class State(TypedDict):
ctx: AppContext
@contextlib.asynccontextmanager
async def lifespan(_app: Starlette) -> AsyncIterator[State]:
pool = await asyncpg.create_pool(os.environ["DATABASE_URL"])
yield {"ctx": AppContext(db=pool)}
await pool.close()
mcp_server = MCPServer(tools=TOOLS, name="my-server", version="1.0.0")
app = Starlette(lifespan=lifespan)
app.mount("/mcp", mcp_server.app)# app/tools.py
from pydantic import BaseModel, Field
from http_mcp.types import Arguments
from app.context import AppContext
class GetUserInput(BaseModel):
user_id: int = Field(description="The user ID to look up")
class GetUserOutput(BaseModel):
name: str = Field(description="The user's name")
email: str = Field(description="The user's email")
async def get_user(args: Arguments[GetUserInput]) -> GetUserOutput:
"""Look up a user by ID."""
ctx = args.get_state_key("ctx", AppContext)
row = await ctx.db.fetchrow(
"SELECT name, email FROM users WHERE id = $1",
args.inputs.user_id,
)
return GetUserOutput(name=row["name"], email=row["email"])Shared HTTP Client
Share a single httpx.AsyncClient across tools to reuse connections and
configure base URLs, headers, or timeouts once:
# app/context.py
from dataclasses import dataclass
import httpx
@dataclass
class AppContext:
http_client: httpx.AsyncClient# app/main.py
import contextlib
from collections.abc import AsyncIterator
from typing import TypedDict
import httpx
from starlette.applications import Starlette
from http_mcp.server import MCPServer
from app.context import AppContext
class State(TypedDict):
ctx: AppContext
@contextlib.asynccontextmanager
async def lifespan(_app: Starlette) -> AsyncIterator[State]:
async with httpx.AsyncClient(
base_url="https://api.example.com",
headers={"Authorization": "Bearer <token>"},
) as client:
yield {"ctx": AppContext(http_client=client)}
mcp_server = MCPServer(tools=TOOLS, name="my-server", version="1.0.0")
app = Starlette(lifespan=lifespan)
app.mount("/mcp", mcp_server.app)# app/tools.py
from pydantic import BaseModel, Field
from http_mcp.types import Arguments
from app.context import AppContext
class SearchInput(BaseModel):
query: str = Field(description="The search query")
class SearchOutput(BaseModel):
results: list[str] = Field(description="Search result titles")
async def search(args: Arguments[SearchInput]) -> SearchOutput:
"""Search via an external API."""
ctx = args.get_state_key("ctx", AppContext)
resp = await ctx.http_client.get("/search", params={"q": args.inputs.query})
resp.raise_for_status()
return SearchOutput(results=[r["title"] for r in resp.json()["items"]])In-Memory Cache
Share mutable state like caches or counters across tool invocations within the same server lifecycle:
# app/context.py
from dataclasses import dataclass, field
@dataclass
class AppContext:
cache: dict[str, str] = field(default_factory=dict)
request_count: int = 0# app/tools.py
from pydantic import BaseModel, Field
from http_mcp.types import Arguments
from app.context import AppContext
class LookupInput(BaseModel):
key: str = Field(description="The cache key to look up")
class LookupOutput(BaseModel):
value: str | None = Field(description="The cached value, or null if not found")
total_requests: int = Field(description="Total requests served")
async def lookup(args: Arguments[LookupInput]) -> LookupOutput:
"""Look up a value in the cache."""
ctx = args.get_state_key("ctx", AppContext)
ctx.request_count += 1
return LookupOutput(
value=ctx.cache.get(args.inputs.key),
total_requests=ctx.request_count,
)All tools sharing the same AppContext instance see each other's writes
immediately, since the lifespan yields a single shared object.
Note: Plain dict and int are not thread-safe. If your tools run concurrently
(e.g., sync tools dispatched via threads), protect shared mutable state with an
asyncio.Lock or use thread-safe data structures.
Request Access
You can access the incoming request object from your tools. The request object is passed to each tool call and can be used to access headers, cookies, and other request data (e.g. request.state, request.scope).
from pydantic import BaseModel, Field
from http_mcp.types import Arguments
class MyToolArguments(BaseModel):
question: str = Field(description="The question to answer")
class MyToolOutput(BaseModel):
answer: str = Field(description="The answer to the question")
async def my_tool(args: Arguments[MyToolArguments]) -> MyToolOutput:
# Access the request
auth_header = args.request.headers.get("Authorization")
...
return MyToolOutput(answer=f"Hello, {args.inputs.question}!")
# Use MCPServer:
from http_mcp.server import MCPServer
mcp_server = MCPServer(
name="my-server",
version="1.0.0",
tools=(my_tool,),
)Prompts
You can add interactive templates that are invoked by user choice. Prompts now support lifespan state access, similar to tools.
Basic Prompt Example
Define the arguments for the prompts:
from pydantic import BaseModel, Field
from http_mcp.types import Arguments, Prompt, PromptMessage, TextContent
class GetAdvice(BaseModel):
topic: str = Field(description="The topic to get advice on")
include_actionable_steps: bool = Field(
description="Whether to include actionable steps in the advice", default=False
)
def get_advice(args: Arguments[GetAdvice]) -> tuple[PromptMessage, ...]:
"""Get advice on a topic."""
template = """
You are a helpful assistant that can give advice on {topic}.
"""
if args.inputs.include_actionable_steps:
template += """
The advice should include actionable steps.
"""
return (
PromptMessage(
role="user",
content=TextContent(
text=template.format(topic=args.inputs.topic)
),
),
)
PROMPTS = (
Prompt(
func=get_advice,
arguments_type=GetAdvice,
),
)Instantiate the server:
from starlette.applications import Starlette
from app.prompts import PROMPTS
from http_mcp.server import MCPServer
app = Starlette()
mcp_server = MCPServer(tools=(), prompts=PROMPTS, name="test", version="1.0.0")
app.mount(
"/mcp",
mcp_server.app,
)Prompts Without Arguments
You can define prompts that don't require any input arguments:
from http_mcp.types import Prompt, PromptMessage, TextContent
def help_prompt() -> tuple[PromptMessage, ...]:
"""Use this prompt to get general help."""
return (
PromptMessage(
role="user",
content=TextContent(
text="You are a helpful assistant. Help the user with their task."
),
),
)
PROMPTS = (
Prompt(
func=help_prompt,
arguments_type=type(None), # No arguments required
),
)Alternatively, you can use the NoArguments class:
from http_mcp.types import Arguments, NoArguments, Prompt, PromptMessage, TextContent
def help_prompt_with_context(args: Arguments[NoArguments]) -> tuple[PromptMessage, ...]:
"""Use this prompt to get help with access to context."""
# You can still access request and state
context = args.get_state_key("context", Context)
return (
PromptMessage(
role="user",
content=TextContent(text="You are a helpful assistant."),
),
)
PROMPTS = (
Prompt(
func=help_prompt_with_context,
arguments_type=NoArguments,
),
)Prompts with Lifespan State
from pydantic import BaseModel, Field
from http_mcp.types import Arguments, Prompt, PromptMessage, TextContent
from app.context import Context
class GetAdvice(BaseModel):
topic: str = Field(description="The topic to get advice on")
def get_advice_with_context(args: Arguments[GetAdvice]) -> tuple[PromptMessage, ...]:
"""Get advice on a topic with context awareness."""
# Access the context from lifespan state
context = args.get_state_key("context", Context)
called_tools = context.get_called_tools()
template = """
You are a helpful assistant that can give advice on {topic}.
Previously called tools: {tools}
"""
return (
PromptMessage(
role="user",
content=TextContent(
text=template.format(
topic=args.inputs.topic,
tools=", ".join(called_tools) if called_tools else "none"
)
)
),
)
PROMPTS_WITH_CONTEXT = (
Prompt(
func=get_advice_with_context,
arguments_type=GetAdvice,
),
)Prompts with Authorization Scopes
You can restrict prompt access based on authentication scopes:
from http_mcp.types import Arguments, NoArguments, Prompt, PromptMessage, TextContent
def private_prompt(args: Arguments[NoArguments]) -> tuple[PromptMessage, ...]:
"""Private prompt that is only accessible to authenticated users."""
return (
PromptMessage(
role="user",
content=TextContent(text="This is a private prompt."),
),
)
def admin_prompt(args: Arguments[NoArguments]) -> tuple[PromptMessage, ...]:
"""Admin prompt accessible to users with admin or superuser scope."""
return (
PromptMessage(
role="user",
content=TextContent(text="This is an admin prompt."),
),
)
PROMPTS = (
Prompt(
func=private_prompt,
arguments_type=NoArguments,
scopes=("private",), # Only accessible with 'private' scope
),
Prompt(
func=admin_prompt,
arguments_type=NoArguments,
scopes=("admin", "superuser"), # Accessible with either scope
),
)Note: You need to set up authentication middleware in your Starlette app for scopes to work properly.
STDIO Transport
In addition to HTTP transport, the server supports STDIO transport for communication. This is useful for command-line applications and integrations that communicate through standard input/output.
Using STDIO Transport
import asyncio
import os
from http_mcp.server import MCPServer
from app.tools import TOOLS
from app.prompts import PROMPTS
mcp_server = MCPServer(
tools=TOOLS,
prompts=PROMPTS,
name="test",
version="1.0.0"
)
# Run the server with STDIO transport
async def main() -> None:
request_headers = {
"Authorization": f"Bearer {os.getenv('MCP_TOKEN', '')}",
"X-Custom-Header": "value",
}
await mcp_server.serve_stdio(request_headers)
asyncio.run(main())The request_headers parameter allows you to pass headers that will be included
in the request context, enabling authentication and other header-based features
even when using STDIO transport.
Authentication and Authorization
The library integrates with Starlette's authentication system to provide scope-based authorization for tools and prompts.
Setting Up Authentication Middleware
import contextlib
from collections.abc import AsyncIterator
from typing import TypedDict
from starlette.applications import Starlette
from starlette.authentication import (
AuthCredentials,
AuthenticationBackend,
BaseUser,
SimpleUser,
)
from starlette.middleware import Middleware
from starlette.middleware.authentication import AuthenticationMiddleware
from starlette.requests import HTTPConnection
from http_mcp.server import MCPServer
from app.context import Context
from app.tools import TOOLS
from app.prompts import PROMPTS
class BasicAuthBackend(AuthenticationBackend):
def __init__(self, granted_scopes: tuple[str, ...] = ("authenticated",)) -> None:
self.granted_scopes = granted_scopes
super().__init__()
async def authenticate(
self, conn: HTTPConnection
) -> tuple[AuthCredentials, BaseUser] | None:
# Implement your authentication logic here
# For example, check Bearer token, API key, etc.
auth_header = conn.headers.get("Authorization")
if not auth_header:
return None
# Validate token and return credentials with scopes
return AuthCredentials(self.granted_scopes), SimpleUser("username")
class State(TypedDict):
context: Context
@contextlib.asynccontextmanager
async def lifespan(_app: Starlette) -> AsyncIterator[State]:
yield {"context": Context()}
mcp_server = MCPServer(
tools=TOOLS,
prompts=PROMPTS,
name="test",
version="1.0.0"
)
app = Starlette(
lifespan=lifespan,
middleware=[
Middleware(
AuthenticationMiddleware,
backend=BasicAuthBackend(granted_scopes=("private", "admin")),
),
],
)
app.mount("/mcp", mcp_server.app)How Scopes Work
Authentication Middleware: The middleware authenticates each request and assigns scopes to the user through
AuthCredentials.Tool/Prompt Scopes: When defining tools or prompts, you can specify required scopes using the
scopesparameter.Access Control: The server automatically filters tools and prompts based on the user's granted scopes. Tools and prompts without the required scopes are not visible in listings and cannot be invoked.
Multiple Scopes: If you specify multiple scopes (e.g.,
scopes=("admin", "superuser")), the user needs at least one of those scopes to access the tool or prompt.
API Reference
Tool Class
The Tool class is used to define tools that can be invoked by clients.
Parameters:
func: The function to be invoked. Can be sync or async. The function can either:Accept an
Arguments[TInputs]parameterAccept no parameters
inputs: The Pydantic model class for input validation. Usetype(None)orNoArgumentsfor tools without inputsoutput: The Pydantic model class for output validationreturn_error_message(bool): IfTrue, tool errors returnErrorMessageinstead of raising exceptions (default:False)scopes(tuple[str, ...]): Required authentication scopes for accessing this tool (default: empty tuple)
Properties:
name: The function name (derived fromfunc.__name__)title: A human-readable title (derived from the function name)description: The function's docstringinput_schema: JSON schema for the input parametersoutput_schema: JSON schema for the output
Prompt Class
The Prompt class is used to define prompts that can be invoked by clients.
Parameters:
func: The function to be invoked. Can be sync or async. The function can either:Accept an
Arguments[TArguments]parameterAccept no parameters
Must return
tuple[PromptMessage, ...]
arguments_type: The Pydantic model class for argument validation. Usetype(None)orNoArgumentsfor prompts without argumentsscopes(tuple[str, ...]): Required authentication scopes for accessing this prompt (default: empty tuple)
Properties:
name: The function name (derived fromfunc.__name__)title: A human-readable title (derived from the function name)description: The function's docstringarguments: Tuple ofPromptArgumentobjects defining the prompt's arguments
Arguments Class
The Arguments class is passed to tool and prompt functions to provide access
to inputs, request, and state.
Parameters:
request: The StarletteRequestobjectinputs: The validated input/argument data (type depends on the Tool/Prompt definition)
Methods:
get_state_key(key: str, _object_type: type[TKey]) -> TKey: Access a value from the lifespan state. RaisesServerErrorif the key doesn't exist.
NoArguments Class
An empty Pydantic model that can be used as a clearer alternative to
type(None) when defining tools or prompts without arguments.
from http_mcp.types import NoArguments
# Use this instead of type(None)
Tool(func=my_func, inputs=NoArguments, output=MyOutput)OAuth 2.1 Authorization (auth_mcp)
The auth_mcp package adds standards-compliant OAuth 2.1 authorization to your
MCP server. Install with the auth extra:
pip install http-mcp[auth]Quick Start
from http_mcp.server import MCPServer
from auth_mcp.resource_server import (
ProtectedMCPAppConfig,
TokenInfo,
TokenValidator,
create_protected_mcp_app,
)
from auth_mcp.types import ProtectedResourceMetadata
class MyTokenValidator(TokenValidator):
async def validate_token(
self, token: str, resource: str | None = None
) -> TokenInfo | None:
# Validate against your authorization server
...
mcp_server = MCPServer(name="my-server", version="1.0.0", tools=MY_TOOLS)
config = ProtectedMCPAppConfig(
mcp_server=mcp_server,
token_validator=MyTokenValidator(),
resource_endpoint=ProtectedResourceMetadata(
resource="https://mcp.example.com",
authorization_servers=("https://auth.example.com",),
),
)
app = create_protected_mcp_app(config)This gives you:
Bearer token validation on all MCP endpoints (secure by default)
/.well-known/oauth-protected-resourcediscovery endpoint (RFC 9728)WWW-Authenticateheaders on 401/403 withresource_metadataparameterSecurity headers (HSTS, nosniff, no-store)
Optional custom middleware via the
middlewaresparameter
For full documentation, best practices, and security surface details, see auth_mcp README.
Security Surfaces by Endpoint
POST /mcp — MCP JSON-RPC Endpoint
Authentication — When using
auth_mcp, Bearer tokens are extracted from theAuthorizationheader and validated viaTokenValidator. Tokens exceeding 2048 characters or containing characters outside the RFC 6750b64tokenpattern are rejected before reaching the validator. Withoutauth_mcp, authentication is handled by Starlette'sAuthenticationMiddleware.Authorization — Scope-based filtering via Starlette's
has_required_scope(). Tools and prompts without matching scopes are hidden from listings and blocked on invocation.Input validation — JSON-RPC messages validated by Pydantic. Request body capped at 4 MB. Content-Type strictly checked (
application/jsononly, media type parameters ignored).Error handling — Tool and prompt names truncated to 100 characters in error messages. Pydantic validation errors sanitized before inclusion in responses.
Response headers —
X-Content-Type-Options: nosniff,Cache-Control: no-storeon all responses.auth_mcpadditionally addsStrict-Transport-Security: max-age=31536000; includeSubDomains.
GET /.well-known/oauth-protected-resource — Discovery Endpoint (auth_mcp)
Authentication — Subject to the same auth middleware as
/mcp. Whenrequire_authentication=True(default), requires a valid token. Set toFalseif clients need to discover the authorization server before authenticating.Input validation — Only
GETallowed; other methods return405 Method Not Allowed.Output — Serialized once at startup from a frozen
ProtectedResourceMetadatamodel. URI fields validated as HTTP/HTTPS URLs via Pydantic'sAnyHttpUrl.
WWW-Authenticate Response Header (auth_mcp)
Header injection — All parameter values (
realm,resource_metadata,scope,error,error_description) are sanitized: CR/LF characters stripped, backslash and double-quote escaped per RFC 7230 quoted-string rules.Information disclosure — Error responses use generic messages (
"Authentication required"). The originalAuthenticationErrordetails are discarded. Error codes (invalid_tokenon 401) follow RFC 6750 without leaking internal state.
STDIO Transport
Message size — Capped at 4 MB, matching HTTP transport.
Logging — Messages truncated to 500 characters in debug logs to prevent log flooding. Token values are never logged.
Headers — Request headers are converted to proper ASGI
list[tuple[bytes, bytes]]format.
Installation
Requires Python 3.12+ (uses PEP 695 type parameter syntax).
Install the package using pip or uv:
pip install http-mcpWith OAuth 2.1 authorization support:
pip install http-mcp[auth]or
uv add http-mcpLicense
This project is licensed under the MIT License. See the LICENSE file for details.
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