Brex MCP Server

Instructions

Implementation Reference

• src/tools/getExpenseById.ts:28-43 (handler)

  Core execution logic for the get_expense tool: parameter validation, Brex API call to retrieve single expense by ID with optional expand fields, returns JSON-formatted response.

  registerToolHandler("get_expense", async (request: ToolCallRequest) => {
    try {
      const params = validateParams(request.params.arguments);
      const client = getBrexClient();
      const expense = await client.getExpense(params.expense_id, { expand: params.expand });
      return {
        content: [{
          type: "text",
          text: JSON.stringify(expense, null, 2)
        }]
      };
    } catch (error) {
      logError(`Error in get_expense: ${error instanceof Error ? error.message : String(error)}`);
      throw error;
    }
  });

• src/tools/getExpenseById.ts:14-25 (schema)

  TypeScript interface and validation function defining the input schema for get_expense: requires expense_id (string), optional expand (string array).

  interface GetExpenseParams {
    expense_id: string;
    expand?: string[];
  }
  
  function validateParams(input: unknown): GetExpenseParams {
    const raw = (input || {}) as Record<string, unknown>;
    if (!raw.expense_id) throw new Error("Missing required parameter: expense_id");
    const out: GetExpenseParams = { expense_id: String(raw.expense_id) };
    if (raw.expand !== undefined) out.expand = Array.isArray(raw.expand) ? raw.expand.map(String) : [String(raw.expand)];
    return out;
  }

• src/tools/getExpenseById.ts:27-44 (registration)

  Registers the get_expense tool handler by calling registerToolHandler with the name and async handler function.

  export function registerGetExpenseById(_server: Server): void {
    registerToolHandler("get_expense", async (request: ToolCallRequest) => {
      try {
        const params = validateParams(request.params.arguments);
        const client = getBrexClient();
        const expense = await client.getExpense(params.expense_id, { expand: params.expand });
        return {
          content: [{
            type: "text",
            text: JSON.stringify(expense, null, 2)
          }]
        };
      } catch (error) {
        logError(`Error in get_expense: ${error instanceof Error ? error.message : String(error)}`);
        throw error;
      }
    });
  }

• src/tools/index.ts:158-167 (schema)

  JSON Schema definition for the get_expense tool input, used in the MCP list_tools response to describe parameters to the LLM.

  name: "get_expense",
  description: "Get a single expense by ID. Returns the complete expense object. Example: {\"expense_id\":\"expense_123\",\"expand\":[\"merchant\"]}",
  inputSchema: {
    type: "object",
    properties: {
      expense_id: { type: "string", description: "Expense ID" },
      expand: { type: "array", items: { type: "string" } }
    },
    required: ["expense_id"]
  }

• src/tools/index.ts:58-58 (registration)

  Invokes the registerGetExpenseById function to add the get_expense tool during server tool registration in registerTools.

  registerGetExpenseById(server);