Expo MCP Server

Instructions

Implementation Reference

• src/file.ts:98-125 (handler)

  The handler function that reads the last N lines from the specified file and returns them as text content.

  export async function tailFile(args: { filePath: string; lines: number }, { log }: LogContext) {
    try {
      log.info(`Tailing file at path: ${args.filePath} (${args.lines} lines)`);
  
      const normalizedPath = path.normalize(args.filePath);
      
      // Read the entire file content
      const fileContent = await fs.promises.readFile(normalizedPath, "utf8");
      
      // Split by newlines and get the last N lines
      const allLines = fileContent.split('\n');
      const lastLines = allLines.slice(-args.lines).join('\n');
  
      log.info(`Successfully tailed ${args.lines} lines from file: ${normalizedPath}`);
  
      return {
        content: [
          {
            type: "text",
            text: lastLines,
          },
        ],
      };
    } catch (error: any) {
      log.error(`Error tailing file: ${error.message}`);
      throw new Error(`Failed to tail file: ${error.message}`);
    }
  }

• src/index.ts:51-54 (schema)

  Zod input schema defining filePath (string) and lines (positive integer).

  parameters: z.object({
    filePath: z.string().describe("The path to the file to tail"),
    lines: z.number().int().positive().describe("Number of lines to read from the end of the file"),
  }),

• src/index.ts:48-56 (registration)

  Registers the tailFile tool with the FastMCP server, specifying name, description, input schema, and handler.

  addTool({
    name: "tailFile",
    description: "Read the last N lines from a file",
    parameters: z.object({
      filePath: z.string().describe("The path to the file to tail"),
      lines: z.number().int().positive().describe("Number of lines to read from the end of the file"),
    }),
    execute: tailFile,
  });