LINE Bot MCP Server

Instructions

Implementation Reference

• src/tools/pushFlexMessage.ts:38-54 (handler)

  The core handler function that validates the userId, pushes the flex message to the LINE API client, and returns success or error response.

  async ({ userId, message }) => {
    if (!userId) {
      return createErrorResponse(NO_USER_ID_ERROR);
    }
  
    try {
      const response = await this.client.pushMessage({
        to: userId,
        messages: [message as unknown as messagingApi.Message],
      });
      return createSuccessResponse(response);
    } catch (error) {
      return createErrorResponse(
        `Failed to push flex message: ${error.message}`,
      );
    }
  },

• src/common/schema/flexMessage.ts:3-22 (schema)

  Zod schema defining the structure of the flex message input, including type, altText, and contents (bubble or carousel).

  export const flexMessageSchema = z.object({
    type: z.literal("flex").default("flex"),
    altText: z
      .string()
      .describe("Alternative text shown when flex message cannot be displayed."),
    contents: z
      .object({
        type: z
          .enum(["bubble", "carousel"])
          .describe(
            "Type of the container. 'bubble' for single container, 'carousel' for multiple swipeable bubbles.",
          ),
      })
      .passthrough()
      .describe(
        "Flexible container structure following LINE Flex Message format. For 'bubble' type, can include header, " +
          "hero, body, footer, and styles sections. For 'carousel' type, includes an array of bubble containers in " +
          "the 'contents' property.",
      ),
  });

• src/tools/pushFlexMessage.ts:30-55 (registration)

  Registers the 'push_flex_message' tool with the MCP server, specifying the name, description, input schema (userId and message), and the handler function.

  server.tool(
    "push_flex_message",
    "Push a highly customizable flex message to a user via LINE. Supports both bubble (single container) and carousel " +
      "(multiple swipeable bubbles) layouts.",
    {
      userId: userIdSchema,
      message: flexMessageSchema,
    },
    async ({ userId, message }) => {
      if (!userId) {
        return createErrorResponse(NO_USER_ID_ERROR);
      }
  
      try {
        const response = await this.client.pushMessage({
          to: userId,
          messages: [message as unknown as messagingApi.Message],
        });
        return createSuccessResponse(response);
      } catch (error) {
        return createErrorResponse(
          `Failed to push flex message: ${error.message}`,
        );
      }
    },
  );

• src/index.ts:62-62 (registration)

  Instantiates the PushFlexMessage class with the messaging API client and destination ID, then calls register to add the tool to the MCP server.

  new PushFlexMessage(messagingApiClient, destinationId).register(server);

• src/tools/pushFlexMessage.ts:23-28 (schema)

  Zod schema for the userId parameter, with default value from destinationId and description.

  const userIdSchema = z
    .string()
    .default(this.destinationId)
    .describe(
      "The user ID to receive a message. Defaults to DESTINATION_USER_ID.",
    );