AI42-MCP X402 Payment Server

Instructions

Implementation Reference

• src/index.ts:120-148 (handler)

  Handler function that sets the global paymentLimit based on input, validates non-negative, and returns confirmation or error.

  async ({ limit }) => {
    try {
      if (limit < 0) {
        throw new Error("Limit must be non-negative");
      }
  
      paymentLimit = limit === 0 ? null : limit;
  
      return {
        content: [{
          type: "text",
          text: JSON.stringify({
            message: paymentLimit === null
              ? "Payment limit removed"
              : `Payment limit set to ${paymentLimit} SOL`,
            current_limit: paymentLimit
          }, null, 2)
        }]
      };
    } catch (err: any) {
      return {
        content: [{
          type: "text",
          text: `Error: ${err.message || "Failed to set payment limit"}`
        }],
        isError: true
      };
    }
  }

• src/index.ts:116-118 (schema)

  Input schema defining the 'limit' parameter as a number with description.

  inputSchema: {
    limit: z.number().describe("Maximum payment amount in SOL (0 to remove limit)")
  },

• src/index.ts:111-149 (registration)

  Registers the 'set-payment-limit' tool with MCP server, including title, description, input schema, and handler reference.

  server.registerTool(
    "set-payment-limit",
    {
      title: "Set Payment Limit",
      description: "Set maximum amount willing to pay per request (in SOL). Set to 0 to remove limit.",
      inputSchema: {
        limit: z.number().describe("Maximum payment amount in SOL (0 to remove limit)")
      },
    },
    async ({ limit }) => {
      try {
        if (limit < 0) {
          throw new Error("Limit must be non-negative");
        }
  
        paymentLimit = limit === 0 ? null : limit;
  
        return {
          content: [{
            type: "text",
            text: JSON.stringify({
              message: paymentLimit === null
                ? "Payment limit removed"
                : `Payment limit set to ${paymentLimit} SOL`,
              current_limit: paymentLimit
            }, null, 2)
          }]
        };
      } catch (err: any) {
        return {
          content: [{
            type: "text",
            text: `Error: ${err.message || "Failed to set payment limit"}`
          }],
          isError: true
        };
      }
    }
  );

• src/index.ts:21-21 (helper)

  Global variable used to store the current payment limit by the handler.

  let paymentLimit: number | null = null;