braintrust

Braintrust JavaScript SDK

An isomorphic JavaScript/TypeScript SDK for logging, tracing, and evaluating AI applications with Braintrust. For more details, see the Braintrust docs

Installation

Install the SDK:

npm install braintrust

Quickstart

Run a simple experiment (replace YOUR_API_KEY with your Braintrust API key):

import * as braintrust from "braintrust";

async function main() {
  const experiment = await braintrust.init("NodeTest", {
    apiKey: "YOUR_API_KEY",
  });

  experiment.log({
    input: { test: 1 },
    output: "foo",
    expected: "bar",
    scores: {
      n: 0.5,
    },
    metadata: {
      id: 1,
    },
  });

  console.log(await experiment.summarize());
}

main().catch(console.error);

Auto-Instrumentation

Braintrust can automatically instrument popular AI SDKs (OpenAI, Anthropic, Vercel AI SDK, and others) to log calls without manual wrapper code.

Node.js

Use the runtime import hook:

node --import braintrust/hook.mjs app.js

Bundled Apps

Use a bundler plugin:

Vite:

import { braintrustVitePlugin } from "braintrust/vite";

export default {
  plugins: [braintrustVitePlugin()],
};

Webpack:

const { braintrustWebpackPlugin } = require("braintrust/webpack");

module.exports = {
  plugins: [braintrustWebpackPlugin()],
};

esbuild:

import { braintrustEsbuildPlugin } from "braintrust/esbuild";

await esbuild.build({
  plugins: [braintrustEsbuildPlugin()],
});

Rollup:

import { braintrustRollupPlugin } from "braintrust/rollup";

export default {
  plugins: [braintrustRollupPlugin()],
};

If you use TypeScript or other transpilation plugins, place the Braintrust plugin after them so transformed output is instrumented.

For deeper details, see the auto-instrumentation architecture docs.

LangSmith tracing

Braintrust supports LangSmith >=0.3.30 <1.0.0. LangSmith tracing remains authoritative: LangSmith must be enabled, and it continues exporting traces to LangSmith while Braintrust mirrors the same run lifecycle. This integration covers tracing only; LangSmith eval, Jest, and Vitest APIs are not instrumented.

For automatic Node.js instrumentation, use the standard hook before importing LangSmith:

node --import braintrust/hook.mjs app.js

The Vite, Webpack, esbuild, and Rollup plugins shown above apply the same automatic instrumentation in bundled applications. To instrument explicit namespaces instead, wrap the three LangSmith entrypoints you use:

import {
  wrapLangSmithClient,
  wrapLangSmithRunTrees,
  wrapLangSmithTraceable,
} from "braintrust";
import * as clientNamespace from "langsmith/client";
import * as runTreesNamespace from "langsmith/run_trees";
import * as traceableNamespace from "langsmith/traceable";

const { Client } = wrapLangSmithClient(clientNamespace);
const { RunTree } = wrapLangSmithRunTrees(runTreesNamespace);
const { traceable } = wrapLangSmithTraceable(traceableNamespace);

The wrappers are composable and idempotent. They preserve LangSmith behavior, including its network export and on_end callbacks. Automatic and explicit instrumentation can safely be used together.

Disable LangSmith instrumentation in code or through the environment:

import { configureInstrumentation } from "braintrust";

configureInstrumentation({ integrations: { langsmith: false } });

BRAINTRUST_DISABLE_INSTRUMENTATION=langsmith node --import braintrust/hook.mjs app.js

When Braintrust LangChain/LangGraph instrumentation is enabled, LangSmith runs serialized by LangChain are ignored to avoid duplicate spans. Set langchain: false (and use LangSmith instrumentation) when LangSmith should be the source for those runs instead.

Migration Guides

Upgrading from 2.x to 3.x

See the Migrate from v2.x to v3.x guide.

In 3.x, browser usage should move to @braintrust/browser instead of relying on the legacy braintrust/browser path.

Upgrading from 1.x to 2.x

See the Migrate from v1.x to v2.x guide.

Upgrading from 0.x to 1.x

See the Migrate from v1.x to v2.x guide.

Compatibility

The braintrust package is compatible with Node.js versions 20.12.0, 22.13.0, for the respective major Node.js release lines and above.