Expo MCP Server

Instructions

Implementation Reference

• src/file.ts:36-59 (handler)

  The writeFile tool handler function. It normalizes the path, creates the directory if necessary, writes the file content using Node.js fs.promises.writeFile, handles errors, logs operations, and returns an MCP-formatted response.

  export async function writeFile(args: { filePath: string; content: string }, { log }: LogContext) {
    try {
      log.info(`Writing to file at path: ${args.filePath}`);
  
      const normalizedPath = path.normalize(args.filePath);
      const directory = path.dirname(normalizedPath);
      await fs.promises.mkdir(directory, { recursive: true });
      await fs.promises.writeFile(normalizedPath, args.content);
  
      log.info(`Successfully wrote to file: ${normalizedPath}`);
  
      return {
        content: [
          {
            type: "text",
            text: `Successfully wrote ${args.content.length} characters to ${normalizedPath}`,
          },
        ],
      };
    } catch (error: any) {
      log.error(`Error writing file: ${error.message}`);
      throw new Error(`Failed to write file: ${error.message}`);
    }
  }

• src/index.ts:27-35 (registration)

  Registration of the writeFile tool on the FastMCP server using addTool. Includes the tool name, description, Zod input schema for parameters, and binding to the execute handler.

  addTool({
    name: "writeFile",
    description: "Write content to a file",
    parameters: z.object({
      filePath: z.string().describe("The path to the file to write"),
      content: z.string().describe("The content to write to the file"),
    }),
    execute: writeFile,
  });

• src/index.ts:30-33 (schema)

  Zod schema definition for the writeFile tool input parameters: filePath (string) and content (string). Used for validation in the MCP tool registration.

  parameters: z.object({
    filePath: z.string().describe("The path to the file to write"),
    content: z.string().describe("The content to write to the file"),
  }),