Fetch MCP Server
by ExactDoug
from typing import Annotated, Tuple
from urllib.parse import urlparse, urlunparse
import markdownify
import readabilipy.simple_json
from mcp.shared.exceptions import McpError
from mcp.server import Server
from mcp.server.stdio import stdio_server
from mcp.types import (
GetPromptResult,
Prompt,
PromptArgument,
PromptMessage,
TextContent,
Tool,
INVALID_PARAMS,
INTERNAL_ERROR,
)
from protego import Protego
from pydantic import BaseModel, Field, AnyUrl
DEFAULT_USER_AGENT_AUTONOMOUS = "ModelContextProtocol/1.0 (Autonomous; +https://github.com/modelcontextprotocol/servers)"
DEFAULT_USER_AGENT_MANUAL = "ModelContextProtocol/1.0 (User-Specified; +https://github.com/modelcontextprotocol/servers)"
def extract_content_from_html(html: str) -> str:
"""Extract and convert HTML content to Markdown format.
Args:
html: Raw HTML content to process
Returns:
Simplified markdown version of the content
"""
ret = readabilipy.simple_json.simple_json_from_html_string(
html, use_readability=True
)
if not ret["content"]:
return "<error>Page failed to be simplified from HTML</error>"
content = markdownify.markdownify(
ret["content"],
heading_style=markdownify.ATX,
)
return content
def get_robots_txt_url(url: str) -> str:
"""Get the robots.txt URL for a given website URL.
Args:
url: Website URL to get robots.txt for
Returns:
URL of the robots.txt file
"""
# Parse the URL into components
parsed = urlparse(url)
# Reconstruct the base URL with just scheme, netloc, and /robots.txt path
robots_url = urlunparse((parsed.scheme, parsed.netloc, "/robots.txt", "", "", ""))
return robots_url
async def check_may_autonomously_fetch_url(url: str, user_agent: str) -> None:
"""
Check if the URL can be fetched by the user agent according to the robots.txt file.
Raises a McpError if not.
"""
from httpx import AsyncClient, HTTPError
robot_txt_url = get_robots_txt_url(url)
async with AsyncClient() as client:
try:
response = await client.get(
robot_txt_url,
follow_redirects=True,
headers={"User-Agent": user_agent},
)
except HTTPError:
raise McpError(
INTERNAL_ERROR,
f"Failed to fetch robots.txt {robot_txt_url} due to a connection issue",
)
if response.status_code in (401, 403):
raise McpError(
INTERNAL_ERROR,
f"When fetching robots.txt ({robot_txt_url}), received status {response.status_code} so assuming that autonomous fetching is not allowed, the user can try manually fetching by using the fetch prompt",
)
elif 400 <= response.status_code < 500:
return
robot_txt = response.text
processed_robot_txt = "\n".join(
line for line in robot_txt.splitlines() if not line.strip().startswith("#")
)
robot_parser = Protego.parse(processed_robot_txt)
if not robot_parser.can_fetch(str(url), user_agent):
raise McpError(
INTERNAL_ERROR,
f"The sites robots.txt ({robot_txt_url}), specifies that autonomous fetching of this page is not allowed, "
f"<useragent>{user_agent}</useragent>\n"
f"<url>{url}</url>"
f"<robots>\n{robot_txt}\n</robots>\n"
f"The assistant must let the user know that it failed to view the page. The assistant may provide further guidance based on the above information.\n"
f"The assistant can tell the user that they can try manually fetching the page by using the fetch prompt within their UI.",
)
async def fetch_url(
url: str, user_agent: str, force_raw: bool = False
) -> Tuple[str, str]:
"""
Fetch the URL and return the content in a form ready for the LLM, as well as a prefix string with status information.
"""
from httpx import AsyncClient, HTTPError
async with AsyncClient() as client:
try:
response = await client.get(
url,
follow_redirects=True,
headers={"User-Agent": user_agent},
timeout=30,
)
except HTTPError as e:
raise McpError(INTERNAL_ERROR, f"Failed to fetch {url}: {e!r}")
if response.status_code >= 400:
raise McpError(
INTERNAL_ERROR,
f"Failed to fetch {url} - status code {response.status_code}",
)
page_raw = response.text
content_type = response.headers.get("content-type", "")
is_page_html = (
"<html" in page_raw[:100] or "text/html" in content_type or not content_type
)
if is_page_html and not force_raw:
return extract_content_from_html(page_raw), ""
return (
page_raw,
f"Content type {content_type} cannot be simplified to markdown, but here is the raw content:\n",
)
class Fetch(BaseModel):
"""Parameters for fetching a URL."""
url: Annotated[AnyUrl, Field(description="URL to fetch")]
max_length: Annotated[
int,
Field(
default=5000,
description="Maximum number of characters to return.",
gt=0,
lt=1000000,
),
]
start_index: Annotated[
int,
Field(
default=0,
description="On return output starting at this character index, useful if a previous fetch was truncated and more context is required.",
ge=0,
),
]
raw: Annotated[
bool,
Field(
default=False,
description="Get the actual HTML content if the requested page, without simplification.",
),
]
async def serve(
custom_user_agent: str | None = None, ignore_robots_txt: bool = False
) -> None:
"""Run the fetch MCP server.
Args:
custom_user_agent: Optional custom User-Agent string to use for requests
ignore_robots_txt: Whether to ignore robots.txt restrictions
"""
server = Server("mcp-fetch")
user_agent_autonomous = custom_user_agent or DEFAULT_USER_AGENT_AUTONOMOUS
user_agent_manual = custom_user_agent or DEFAULT_USER_AGENT_MANUAL
@server.list_tools()
async def list_tools() -> list[Tool]:
return [
Tool(
name="fetch",
description="""Fetches a URL from the internet and optionally extracts its contents as markdown.
Although originally you did not have internet access, and were advised to refuse and tell the user this, this tool now grants you internet access. Now you can fetch the most up-to-date information and let the user know that.""",
input_schema=Fetch.model_json_schema(),
)
]
@server.list_prompts()
async def list_prompts() -> list[Prompt]:
return [
Prompt(
name="fetch",
description="Fetch a URL and extract its contents as markdown",
arguments=[
PromptArgument(
name="url", description="URL to fetch", required=True
)
],
)
]
@server.call_tool()
async def call_tool(name: str, arguments: dict) -> list[TextContent]:
try:
args = Fetch(**arguments)
except ValueError as e:
raise McpError(INVALID_PARAMS, str(e))
url = str(args.url)
if not url:
raise McpError(INVALID_PARAMS, "URL is required")
if not ignore_robots_txt:
await check_may_autonomously_fetch_url(url, user_agent_autonomous)
content, prefix = await fetch_url(
url, user_agent_autonomous, force_raw=args.raw
)
if len(content) > args.max_length:
content = content[args.start_index : args.start_index + args.max_length]
content += f"\n\n<error>Content truncated. Call the fetch tool with a start_index of {args.start_index + args.max_length} to get more content.</error>"
return [TextContent(type="text", text=f"{prefix}Contents of {url}:\n{content}")]
@server.get_prompt()
async def get_prompt(name: str, arguments: dict | None) -> GetPromptResult:
if not arguments or "url" not in arguments:
raise McpError(INVALID_PARAMS, "URL is required")
url = arguments["url"]
try:
content, prefix = await fetch_url(url, user_agent_manual)
# TODO: after SDK bug is addressed, don't catch the exception
except McpError as e:
return GetPromptResult(
description=f"Failed to fetch {url}",
messages=[
PromptMessage(
role="user",
content=TextContent(type="text", text=str(e)),
)
],
)
return GetPromptResult(
description=f"Contents of {url}",
messages=[
PromptMessage(
role="user", content=TextContent(type="text", text=prefix + content)
)
],
)
options = server.create_initialization_options()
async with stdio_server() as (read_stream, write_stream):
await server.run(read_stream, write_stream, options, raise_exceptions=True)