fetch_json
Retrieve JSON data from a URL by specifying the source address, optional headers, and content length parameters for web content integration.
Instructions
Fetch a JSON file from a URL
Input Schema
TableJSON Schema
| Name | Required | Description | Default |
|---|---|---|---|
| url | Yes | URL of the JSON to fetch | |
| headers | No | Optional headers to include in the request | |
| max_length | No | Maximum number of characters to return (default: 5000) | |
| start_index | No | Start content from this character index (default: 0) |
Implementation Reference
- src/Fetcher.ts:67-89 (handler)Core handler logic for 'fetch_json': fetches URL, parses JSON, stringifies it, applies length limits, returns formatted content or error.static async json(requestPayload: RequestPayload) { try { const response = await this._fetch(requestPayload); const json = await response.json(); let jsonString = JSON.stringify(json); // Apply length limits jsonString = this.applyLengthLimits( jsonString, requestPayload.max_length ?? 5000, requestPayload.start_index ?? 0 ); return { content: [{ type: "text", text: jsonString }], isError: false, }; } catch (error) { return { content: [{ type: "text", text: (error as Error).message }], isError: true, }; }
- src/types.ts:5-10 (schema)Zod schema for validating input parameters to 'fetch_json' and other fetch 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/index.ts:109-134 (registration)Tool registration in ListTools handler, defining name, description, and input schema for 'fetch_json'.{ name: "fetch_json", description: "Fetch a JSON file from a URL", inputSchema: { type: "object", properties: { url: { type: "string", description: "URL of the JSON 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:148-150 (handler)Dispatch logic in CallToolRequest handler that routes 'fetch_json' calls to Fetcher.json.if (request.params.name === "fetch_json") { const fetchResult = await Fetcher.json(validatedArgs); return fetchResult;
- src/Fetcher.ts:15-44 (helper)Shared helper method for performing the HTTP fetch with security checks and error handling, used by 'fetch_json'.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`); } } }