Fetch MCP Server

Instructions

Implementation Reference

• src/Fetcher.ts:46-65 (handler)

  Core handler function that fetches HTML content using _fetch, applies length limits, and formats the response for MCP.
  static async html(requestPayload: RequestPayload) { try { const response = await this._fetch(requestPayload); let html = await response.text(); // Apply length limits html = this.applyLengthLimits( html, requestPayload.max_length ?? 5000, requestPayload.start_index ?? 0 ); return { content: [{ type: "text", text: html }], isError: false }; } catch (error) { return { content: [{ type: "text", text: (error as Error).message }], isError: true, }; } }
• src/index.ts:31-55 (registration)

  Tool registration in ListToolsRequest handler, defining name, description, and input schema.
  name: "fetch_html", description: "Fetch a website and return its unmodified contents as HTML", inputSchema: { type: "object", properties: { url: { type: "string", description: "URL of the website to fetch", }, headers: { type: "object", description: "Optional headers to include in the request", }, max_length: { type: "number", description: `Maximum number of characters to return (default: ${downloadLimit})`, }, start_index: { type: "number", description: "Start content from this character index (default: 0)", }, }, required: ["url"], }, },
• src/index.ts:144-147 (handler)

  Dispatch logic in CallToolRequest handler that invokes Fetcher.html for 'fetch_html' tool calls.
  if (request.params.name === "fetch_html") { const fetchResult = await Fetcher.html(validatedArgs); return fetchResult; }
• src/types.ts:5-10 (schema)

  Zod schema used to validate input arguments for fetch_html and other tools.
  export const RequestPayloadSchema = z.object({ url: z.string().url(), headers: z.record(z.string()).optional(), max_length: z.number().int().min(0).optional().default(downloadLimit), start_index: z.number().int().min(0).optional().default(0), });
• src/Fetcher.ts:15-44 (helper)

  Private helper method for performing the actual fetch request with security checks and error handling.
  private static async _fetch({ url, headers, }: RequestPayload): Promise<Response> { try { if (is_ip_private(url)) { throw new Error( `Fetcher blocked an attempt to fetch a private IP ${url}. This is to prevent a security vulnerability where a local MCP could fetch privileged local IPs and exfiltrate data.`, ); } const response = await fetch(url, { headers: { "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36", ...headers, }, }); if (!response.ok) { throw new Error(`HTTP error: ${response.status}`); } return response; } catch (e: unknown) { if (e instanceof Error) { throw new Error(`Failed to fetch ${url}: ${e.message}`); } else { throw new Error(`Failed to fetch ${url}: Unknown error`); } } }