fetch
Retrieve and convert web content to markdown with internet access, extracting data from URLs up to a specified character limit or starting index for expanded context.
Instructions
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
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| max_length | No | Maximum number of characters to return. | |
| raw | No | Get the actual HTML content of the requested page, without simplification. | |
| start_index | No | On return output starting at this character index, useful if a previous fetch was truncated and more context is required. | |
| url | Yes | URL to fetch |
Implementation Reference
- src/context_mcp_server/server.py:257-286 (handler)Handler logic for the 'fetch' tool call within the MCP server's call_tool decorator. Parses arguments using Fetch schema, fetches content via fetch_url helper, applies truncation based on max_length and start_index, and returns TextContent.if name == "fetch": try: args = Fetch(**arguments) except ValueError as e: raise McpError(ErrorData(code=INVALID_PARAMS, message=str(e))) url = str(args.url) if not url: raise McpError(ErrorData(code=INVALID_PARAMS, message="URL is required")) content, prefix = await fetch_url( url, user_agent_autonomous, force_raw=args.raw, proxy_url=proxy_url ) original_length = len(content) if args.start_index >= original_length: content = "<error>No more content available.</error>" else: truncated_content = content[args.start_index : args.start_index + args.max_length] if not truncated_content: content = "<error>No more content available.</error>" else: content = truncated_content actual_content_length = len(truncated_content) remaining_content = original_length - (args.start_index + actual_content_length) # Only add the prompt to continue fetching if there is still remaining content if actual_content_length == args.max_length and remaining_content > 0: next_start = args.start_index + actual_content_length content += f"\n\n<error>Content truncated. Call the fetch tool with a start_index of {next_start} to get more content.</error>" return [TextContent(type="text", text=f"{prefix}Contents of {url}:\n{content}")]
- Pydantic schema (BaseModel) defining input parameters for the 'fetch' tool: url, max_length, start_index, raw.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 of the requested page, without simplification.", ), ]
- src/context_mcp_server/server.py:225-231 (registration)Tool registration in the MCP server's list_tools() method, specifying name='fetch', description, and inputSchema from Fetch model.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.""", inputSchema=Fetch.model_json_schema(), ),
- Core helper function that performs the actual HTTP fetch using httpx.AsyncClient, detects HTML and simplifies to markdown using extract_content_from_html if applicable, returns content and prefix.async def fetch_url( url: str, user_agent: str, force_raw: bool = False, proxy_url: str | None = None ) -> 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(proxies=proxy_url) as client: try: response = await client.get( url, follow_redirects=True, headers={"User-Agent": user_agent}, timeout=30, ) except HTTPError as e: raise McpError(ErrorData(code=INTERNAL_ERROR, message=f"Failed to fetch {url}: {e!r}")) if response.status_code >= 400: raise McpError(ErrorData( code=INTERNAL_ERROR, message=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", )