Server overview

Mastra runs as an HTTP server that exposes your agents, workflows, and other functionality as API endpoints. The server handles request routing, middleware execution, authentication, and streaming responses.

info

This page covers the server configuration options passed to the Mastra constructor. For running Mastra with your own HTTP server (Hono, Express, etc.), visit Server Adapters.

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 and workflows
• Custom API routes and middleware
• Authentication across providers
• Request context for dynamic configuration
• Stream data redaction for secure responses

Configuration

Configure the server by passing a server object to the Mastra constructor:

src/mastra/index.ts

import { Mastra } from '@mastra/core'

export const mastra = new Mastra({
  server: {
    port: 3000, // Defaults to PORT env var or 4111
    host: '0.0.0.0', // Defaults to MASTRA_HOST env var or 'localhost'
  },
})

info

Visit the configuration reference for a full list of available server options.

Server features

• Middleware: Intercept requests for authentication, logging, CORS, or injecting request-specific context.
• Custom API Routes: Extend the server with your own HTTP endpoints that have access to the Mastra instance.
• Request Context: Pass request-specific values to agents, tools, and workflows based on runtime conditions.
• Server Adapters: Run Mastra with Express, Hono, or your own HTTP server instead of the generated server.
• Custom Adapters: Build adapters for frameworks not officially supported.
• Mastra Client SDK: Type-safe client for calling agents, workflows, and tools from browser or server environments.
• Authentication: Secure endpoints with JWT, Clerk, Supabase, Firebase, Auth0, or WorkOS.

REST API

You can explore all available endpoints in the OpenAPI specification at http://localhost:4111/api/openapi.json, which details every endpoint and its request and response schemas.

To explore the API interactively, visit the Swagger UI at http://localhost:4111/swagger-ui. Here, you can discover endpoints and test them directly from your browser.

note

The OpenAPI and Swagger endpoints are disabled in production by default. To enable them, set server.build.openAPIDocs and server.build.swaggerUI to true respectively.

OpenAI Responses API

Mastra exposes OpenAI-compatible Responses and Conversations routes that let you use Mastra Agents as a Responses API. These routes are agent-backed adapters over Mastra agents, memory, and storage, so requests run through the selected Mastra agent instead of acting as a raw provider proxy.

These APIs are currently experimental.

Use agent_id to select the Mastra agent that should handle the request. Initial requests target an agent directly, and stored follow-up turns can continue with previous_response_id. You can also pass model to override the agent's configured model for a single request. If you omit model, Mastra uses the model already configured on the agent.

The Responses routes support streaming, function calling (tools), stored continuations with previous_response_id, conversation threads through conversation_id, provider-specific passthrough with providerOptions, and JSON output through text.format.

For the full request and response contract, see the Responses API reference and Conversations API reference. For the complete list of HTTP routes, see server routes.

Stream data redaction

When streaming agent responses, the HTTP layer redacts system prompts, tool definitions, API keys, and similar data from each chunk before sending it to clients. This is enabled by default.

This behavior is only configurable by using server adapters. For server adapters, stream data redaction is enabled by default, too.

TypeScript configuration

Mastra requires module and moduleResolution settings compatible with modern Node.js. Legacy options like CommonJS or node aren't supported.

tsconfig.json

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "ES2022",
    "moduleResolution": "bundler",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true,
    "noEmit": true,
    "outDir": "dist"
  },
  "include": ["src/**/*"]
}