Mastra is a TypeScript framework that wraps the Vercel AI SDK with its own primitives: typed createTool definitions with input and output schemas, a top-level Mastra registry that wires agents into storage and observability, a Model Router that turns 'anthropic/claude-haiku-4-5' into a working client without a provider package install, and a built-in Studio playground (mastra dev) for chatting with your agents and replaying traces. The Steel integration runs each tool against a Steel cloud session, so the agent's tool surface is "drive a real browser" without leaving the Mastra primitives.

Requirements

• Steel API Key: Active Steel subscription
• Node.js: v22.13+
• Packages: @mastra/core, steel-sdk, playwright, zod
• Model provider key: Anthropic, OpenAI, Google, or any other provider supported by the Mastra Model Router

Connect Steel to Mastra

Define a createTool that opens a Steel session, register it on an Agent, and attach the agent to a top-level Mastra registry:

import { Mastra } from "@mastra/core";
import { Agent } from "@mastra/core/agent";
import { createTool } from "@mastra/core/tools";
import { chromium } from "playwright";
import Steel from "steel-sdk";
import { z } from "zod";

const steel = new Steel({ steelAPIKey: process.env.STEEL_API_KEY! });

const openSession = createTool({
  id: "open-session",
  description: "Open a Steel cloud browser session.",
  inputSchema: z.object({}),
  outputSchema: z.object({
    sessionId: z.string(),
    liveViewUrl: z.string(),
  }),
  execute: async () => {
    const session = await steel.sessions.create({});
    const browser = await chromium.connectOverCDP(
      `${session.websocketUrl}&apiKey=${process.env.STEEL_API_KEY}`,
    );
    return { sessionId: session.id, liveViewUrl: session.sessionViewerUrl };
  },
});

const researchAgent = new Agent({
  id: "research-agent",
  name: "Steel Research",
  instructions: "You operate a Steel cloud browser via tools. ...",
  model: "anthropic/claude-haiku-4-5",
  tools: { openSession },
});

export const mastra = new Mastra({ agents: { researchAgent } });

Tools are passed as a record (not an array): the keys are what the model sees as tool names. With the registry wired up, npx mastra dev opens Studio at http://localhost:4111 so you can chat with research-agent and inspect its tool calls live.

Full runnable starter: Steel + Mastra recipe →

Resources

• Mastra documentation – Agents, tools, workflows, memory, and Studio
• Mastra Model Router – Provider-agnostic model strings
• Mastra Studio – Local playground for agents and workflows
• Steel Sessions API reference – Programmatic session control for Steel browsers
• Steel Discord – Get help and share what you build