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Mastra is a TypeScript framework for building AI agents. Braintrust integrates with Mastra’s observability system to automatically trace agent executions, LLM calls, and tool usage.

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Setup

Install Mastra with the Braintrust exporter: 
# pnpm
pnpm add @mastra/core @mastra/braintrust @mastra/observability braintrust
# npm
npm install @mastra/core @mastra/braintrust @mastra/observability braintrust

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Trace with Mastra

Braintrust traces Mastra agent runs, workflows, steps, tool calls, and LLM calls. Enable tracing without code changes through auto-instrumentation, or configure a Braintrust exporter manually.

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Auto-instrumentation

To trace Mastra without modifying your application code, run your app with Braintrust’s import hook. The hook adds a Braintrust exporter to Mastra’s observability automatically, so you don’t configure one yourself. Requires @mastra/core v1.20.0 or later and the @mastra/observability package.
1

Build your Mastra app

mastra-app.js
import { initLogger } from "braintrust";
import { Mastra } from "@mastra/core";
import { Agent } from "@mastra/core/agent";

initLogger({
  projectName: "mastra-demo", // Replace with your project name
  apiKey: process.env.BRAINTRUST_API_KEY,
});

const mastra = new Mastra({
  agents: {
    assistant: new Agent({
      name: "Assistant",
      instructions: "You only respond in haikus.",
      model: "openai/gpt-5-mini",
    }),
  },
});

const response = await mastra
  .getAgent("assistant")
  .generate("Tell me about recursion in programming.");
console.log(response.text);
2

Run with the import hook

node --import braintrust/hook.mjs mastra-app.js
The auto-instrumentation example uses plain JavaScript so node --import can run the file directly. The Braintrust APIs work the same in TypeScript projects — compile your TypeScript to JavaScript, then run the compiled file with the import hook.
If you’re using a bundler, see Trace LLM calls for plugin and loader setup.

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Manual instrumentation

To configure tracing explicitly, add a Braintrust exporter to Mastra’s Observability settings yourself. Use the BraintrustObservabilityExporter built into the braintrust SDK:
trace-mastra.ts
import { Agent } from "@mastra/core/agent";
import { Mastra } from "@mastra/core/mastra";
import { Observability } from "@mastra/observability";
import { BraintrustObservabilityExporter, initLogger } from "braintrust";

initLogger({ projectName: "mastra-demo" });

const mastra = new Mastra({
  agents: {
    assistant: new Agent({
      name: "Assistant",
      instructions: "You only respond in haikus.",
      model: "openai/gpt-5-mini",
    }),
  },
  observability: new Observability({
    configs: {
      braintrust: {
        serviceName: "mastra-demo",
        exporters: [new BraintrustObservabilityExporter()],
      },
    },
  }),
});
Alternatively, use the BraintrustExporter from the Mastra-maintained @mastra/braintrust package, which accepts a Braintrust logger directly:
trace-mastra-exporter.ts
import { Agent } from "@mastra/core/agent";
import { Mastra } from "@mastra/core/mastra";
import { Observability } from "@mastra/observability";
import { BraintrustExporter } from "@mastra/braintrust";
import { initLogger } from "braintrust";

const logger = initLogger({ projectName: "mastra-demo" });

const exporter = new BraintrustExporter({
  braintrustLogger: logger,
});

const mastra = new Mastra({
  agents: {
    assistant: new Agent({
      name: "Assistant",
      instructions: "You only respond in haikus.",
      model: "openai/gpt-4o-mini",
    }),
  },
  observability: new Observability({
    configs: {
      braintrust: {
        serviceName: "demo",
        exporters: [exporter],
      },
    },
  }),
});

async function main() {
  const agent = mastra.getAgent("assistant");
  const response = await agent.generate("Tell me about recursion in programming.");
  console.log(response.text);
}

main();
The BraintrustExporter constructor can accept a braintrust.Span, braintrust.Experiment, or braintrust.Logger as the braintrustLogger option. This enables automatic nesting of Mastra traces within Braintrust contexts like evals or traced functions.

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What Braintrust traces

Braintrust captures:
  • Agent run spans (agent run: <name>) and workflow run spans (workflow run: <name>) as task spans, with inputs and outputs.
  • LLM spans (llm: <model>) for model generations, with the messages as input and the response as output.
  • Workflow step spans (workflow step: <id>) and tool call spans for the steps and tools an agent or workflow runs.
  • Token usage metrics (prompt, completion, total, plus cached, cache-creation, and reasoning tokens when reported) on LLM spans.
  • Span metadata, including entity_id, entity_name, and entity_type, plus the model and provider on LLM spans.
  • Errors captured on every span.

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Evaluate with Mastra

Use Mastra agents as the task in a Braintrust Eval to build and evaluate agentic workflows:
eval-mastra.ts
import { Agent } from "@mastra/core/agent";
import { Mastra } from "@mastra/core/mastra";
import { Observability } from "@mastra/observability";
import { BraintrustExporter } from "@mastra/braintrust";
import { Eval, initLogger } from "braintrust";

const logger = initLogger({ projectName: "mastra-demo" });

const exporter = new BraintrustExporter({
  braintrustLogger: logger,
});

const mastra = new Mastra({
  agents: {
    assistant: new Agent({
      name: "Assistant",
      instructions: "You only respond in haikus.",
      model: "openai/gpt-4o-mini",
    }),
  },
  observability: new Observability({
    configs: {
      braintrust: {
        serviceName: "demo",
        exporters: [exporter],
      },
    },
  }),
});

Eval('mastra-demo', {
  data: () => [
    { input: 'What is the capital of France?', expected: 'Paris' },
    { input: 'What is 2+2?', expected: '4' },
  ],
  task: async (input: string) => {
    const agent = mastra.getAgent('assistant');
    return (await agent.generate(input)).text;
  },
  scores: [
    (args: { output: string; expected: string }) => ({
      name: 'contains_answer',
      score: String(args.output).toLowerCase().includes(String(args.expected).toLowerCase()) ? 1 : 0,
    }),
  ],
});

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