YNAB MCP Server

Instructions

Implementation Reference

• src/tools/BudgetSummaryTool.ts:25-59 (handler)

  The main handler function that fetches active accounts and categories for the specified budget month and returns a JSON summary, handling errors gracefully.

  export async function execute(input: BudgetSummaryInput, api: ynab.API) {
    try {
      const budgetId = getBudgetId(input.budgetId);
      const month = input.month || "current";
  
      console.error(`Getting accounts and categories for budget ${budgetId} and month ${month}`);
      const accountsResponse = await api.accounts.getAccounts(budgetId);
      const accounts = accountsResponse.data.accounts.filter(
        (account) => account.deleted === false && account.closed === false
      );
  
      const monthBudget = await api.months.getBudgetMonth(budgetId, month);
  
      const categories = monthBudget.data.month.categories
        .filter(
          (category) => category.deleted === false && category.hidden === false
        );
  
      return {
        content: [{ type: "text" as const, text: JSON.stringify({
          monthBudget: monthBudget.data.month,
          accounts: accounts,
          note: "Divide all numbers by 1000 to get the balance in dollars.",
        }, null, 2) }]
      };
    } catch (error: unknown) {
      console.error("Error getting budget summary:", error);
      return {
        content: [{ type: "text" as const, text: JSON.stringify({
          success: false,
          error: getErrorMessage(error),
        }, null, 2) }]
      };
    }
  }

• src/tools/BudgetSummaryTool.ts:5-10 (schema)

  Exports the tool name, description, and Zod input schema defining optional budgetId and month parameters.

  export const name = "ynab_budget_summary";
  export const description = "Get a summary of the budget for a specific month highlighting overspent categories that need attention and categories with a positive balance that are doing well.";
  export const inputSchema = {
    budgetId: z.string().optional().describe("The ID of the budget to get a summary for (optional, defaults to the budget set in the YNAB_BUDGET_ID environment variable)"),
    month: z.string().regex(/^(current|\d{4}-\d{2}-\d{2})$/).default("current").describe("The budget month in ISO format (e.g. 2016-12-01). The string 'current' can also be used to specify the current calendar month (UTC)"),
  };

• src/index.ts:45-49 (registration)

  Registers the ynab_budget_summary tool with the MCP server using the imported name, description, inputSchema, and a wrapper around the execute handler.

  server.registerTool(BudgetSummaryTool.name, {
    title: "Budget Summary",
    description: BudgetSummaryTool.description,
    inputSchema: BudgetSummaryTool.inputSchema,
  }, async (input) => BudgetSummaryTool.execute(input, api));

• src/tools/BudgetSummaryTool.ts:17-23 (helper)

  Helper function to retrieve the budget ID from input or environment variable, throwing an error if not available.

  function getBudgetId(inputBudgetId?: string): string {
    const budgetId = inputBudgetId || process.env.YNAB_BUDGET_ID || "";
    if (!budgetId) {
      throw new Error("No budget ID provided. Please provide a budget ID or set the YNAB_BUDGET_ID environment variable.");
    }
    return budgetId;
  }