Currency Converter MCP

Implementation Reference

• src/tools/get_latest_rates.ts:29-73 (handler)

  The handler function that fetches the latest exchange rates from the Frankfurter API using the provided base currency and symbols, handles errors, and returns the response as a ToolResponse.

  export async function getLatestRates(
  	input: GetLatestRatesInput,
  ): Promise<ToolResponse> {
  	const { base, symbols } = input;
  
  	try {
  		const params = new URLSearchParams();
  		if (base) params.append("base", base.toUpperCase());
  		if (symbols) params.append("symbols", symbols.toUpperCase());
  
  		const url = `${FRANKFURTER_API_BASE}/latest${params.toString() ? `?${params.toString()}` : ""}`;
  		const response = await fetch(url);
  
  		if (!response.ok) {
  			return {
  				content: [
  					{
  						type: "text",
  						text: `Error: Unable to fetch exchange rates. Status: ${response.status}`,
  					},
  				],
  			};
  		}
  
  		const data = (await response.json()) as ExchangeRateResponse;
  
  		return {
  			content: [
  				{
  					type: "text",
  					text: JSON.stringify(data),
  				},
  			],
  		};
  	} catch (error) {
  		return {
  			content: [
  				{
  					type: "text",
  					text: `Error: Failed to fetch exchange rates - ${error instanceof Error ? error.message : "Unknown error"}`,
  				},
  			],
  		};
  	}
  }

• src/tools/get_latest_rates.ts:8-20 (schema)

  Input schema using Zod for validating base currency (optional, 3-letter code) and symbols (optional comma-separated list).

  export const getLatestRatesSchema = {
  	base: z
  		.string()
  		.length(3)
  		.optional()
  		.describe("Base currency code (default: EUR)"),
  	symbols: z
  		.string()
  		.optional()
  		.describe(
  			"Comma-separated currency codes to limit results (e.g., USD,GBP,JPY)",
  		),
  };

• src/index.ts:29-31 (registration)

  Registers the 'get_latest_rates' tool with the MCP server, providing the schema and handler function.

  this.server.tool("get_latest_rates", getLatestRatesSchema, async (input) =>
    getLatestRates(input),
  );