Creating A Mastra Server

While developing or when you deploy a Mastra application, it runs as an HTTP server that exposes your agents, workflows, and other functionality as API endpoints. This page explains how to configure and customize the server behavior.

Server Architecture

Mastra uses Hono as its underlying HTTP server framework. When you build a Mastra application using mastra build, it generates a Hono-based HTTP server in the .mastra directory.

The server provides:

API endpoints for all registered agents
API endpoints for all registered workflows
Custom api route supports
Custom middleware support
Configuration of timeout
Configuration of port

Server configuration

You can configure server port and timeout in the Mastra instance.


import { Mastra } from "@mastra/core";
 
export const mastra = new Mastra({
  server: {
    port: 3000, // Defaults to 4111
    timeout: 10000, // Defaults to 30000 (30s)
  },
});

Custom API Routes

Mastra provides a list of api routes that are automatically generated based on the registered agents and workflows. You can also define custom api routes on the Mastra instance.

These routes can live in the same file as the Mastra instance or in a separate file. We recommend keeping them in a separate file to keep the Mastra instance clean.


import { Mastra } from "@mastra/core";
import { registerApiRoute } from "@mastra/core/server";
 
export const mastra = new Mastra({
  server: {
    apiRoutes: [
      registerApiRoute("/my-custom-route", {
        method: "GET",
        handler: async (c) => {
          // you have access to mastra instance here
          const mastra = c.get("mastra");
 
          // you can use the mastra instance to get agents, workflows, etc.
          const agents = await mastra.getAgent("my-agent");
 
          return c.json({ message: "Hello, world!" });
        },
      }),
    ],
  },
  // Other configuration options
});

Custom CORS Config

Mastra allows you to configure CORS (Cross-Origin Resource Sharing) settings for your server.


import { Mastra } from '@mastra/core';
 
export const mastra = new Mastra({
  server: {
    cors: {
      origin: ['https://example.com'], // Allow specific origins or '*' for all
      allowMethods: ['GET', 'POST', 'PUT', 'DELETE', 'OPTIONS'],
      allowHeaders: ['Content-Type', 'Authorization'],
      credentials: false,
    }
  }
});

Middleware

Mastra allows you to configure custom middleware functions that will be applied to API routes. This is useful for adding authentication, logging, CORS, or other HTTP-level functionality to your API endpoints.


import { Mastra } from '@mastra/core';
 
export const mastra = new Mastra({
  // Other configuration options
  server: {
    middleware: [
    {
      handler: async (c, next) => {
        // Example: Add authentication check
        const authHeader = c.req.header('Authorization');
        if (!authHeader) {
          return new Response('Unauthorized', { status: 401 });
        }
 
        // Continue to the next middleware or route handler
        await next();
      },
      path: '/api/*'
    },
    // add middleware to all routes
    async (c, next) => {
      // Example: Add request logging
      console.log(`${c.req.method} ${c.req.url}`);
      await next();
    },
  ]
});

if you want to add a middleware to a single route, you can also specify that in the registerApiRoute using registerApiRoute.


registerApiRoute("/my-custom-route", {
  method: "GET",
  middleware: [
    async (c, next) => {
      // Example: Add request logging
      console.log(`${c.req.method} ${c.req.url}`);
      await next();
    },
  ],
  handler: async (c) => {
    // you have access to mastra instance here
    const mastra = c.get("mastra");
 
    // you can use the mastra instance to get agents, workflows, etc.
    const agents = await mastra.getAgent("my-agent");
 
    return c.json({ message: "Hello, world!" });
  },
});

Middleware Behavior

Each middleware function:

Receives a Hono context object (c) and a next function
Can return a Response to short-circuit the request handling
Can call next() to continue to the next middleware or route handler
Can optionally specify a path pattern (defaults to ‘/api/*’)
Inject request specific data for agent tool calling or workflows

Common Middleware Use Cases

Authentication


{
  handler: async (c, next) => {
    const authHeader = c.req.header('Authorization');
    if (!authHeader || !authHeader.startsWith('Bearer ')) {
      return new Response('Unauthorized', { status: 401 });
    }
 
    const token = authHeader.split(' ')[1];
    // Validate token here
 
    await next();
  },
  path: '/api/*',
}

CORS Support


{
  handler: async (c, next) => {
    // Add CORS headers
    c.header("Access-Control-Allow-Origin", "*");
    c.header("Access-Control-Allow-Methods", "GET, POST, PUT, DELETE, OPTIONS");
    c.header("Access-Control-Allow-Headers", "Content-Type, Authorization");
 
    // Handle preflight requests
    if (c.req.method === "OPTIONS") {
      return new Response(null, { status: 204 });
    }
 
    await next();
  };
}

Request Logging


{
  handler: async (c, next) => {
    const start = Date.now();
    await next();
    const duration = Date.now() - start;
    console.log(`${c.req.method} ${c.req.url} - ${duration}ms`);
  };
}

Special Mastra Headers

When integrating with Mastra Cloud or building custom clients, there are special headers that clients send to identify themselves and enable specific features. Your server middleware can check for these headers to customize behavior:


{
  handler: async (c, next) => {
    // Check for Mastra-specific headers in incoming requests
    const isFromMastraCloud = c.req.header("x-mastra-cloud") === "true";
    const clientType = c.req.header("x-mastra-client-type"); // e.g., 'js', 'python'
    const isDevPlayground = c.req.header("x-mastra-dev-playground") === "true";
 
    // Customize behavior based on client information
    if (isFromMastraCloud) {
      // Special handling for Mastra Cloud requests
    }
 
    await next();
  };
}

These headers have the following purposes:

x-mastra-cloud: Indicates that the request is coming from Mastra Cloud
x-mastra-client-type: Specifies the client SDK type (e.g., ‘js’, ‘python’)
x-mastra-dev-playground: Indicates that the request is from the development playground

You can use these headers in your middleware to implement client-specific logic or enable features only for certain environments.

Deployment

Since Mastra builds to a standard Node.js server, you can deploy to any platform that runs Node.js applications:

Cloud VMs (AWS EC2, DigitalOcean Droplets, GCP Compute Engine)
Container platforms (Docker, Kubernetes)
Platform as a Service (Heroku, Railway)
Self-hosted servers

Building

Build the application:


# Build from current directory
mastra build
 
# Or specify a directory
mastra build --dir ./my-project

The build process:

Locates entry file (src/mastra/index.ts or src/mastra/index.js)
Creates .mastra output directory
Bundles code using Rollup with tree shaking and source maps
Generates Hono HTTP server

See mastra build for all options.

Running the Server

Start the HTTP server:


node .mastra/output/index.mjs

Serverless Deployment

Mastra also supports serverless deployment on Cloudflare Workers, Vercel, and Netlify.

See our Serverless Deployment guide for setup instructions.