@langfuse/browser

Langfuse is the open-source LLM engineering platform: tracing & evaluation for LLM and agent applications, prompt management, datasets & experiments, and evaluation (scores). This package provides the browser client for score ingestion only — e.g. capturing end-user feedback (thumbs up/down, ratings) from the frontend and attaching it to traces. It authenticates with the public key alone, so it is safe to ship to browsers. Everything else (tracing, prompt management, datasets/experiments, full API access) requires a secret key and lives in the server-side packages @langfuse/tracing, @langfuse/otel, and @langfuse/client.

Install

npm install @langfuse/browser
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Quickstart

import { LangfuseBrowserClient } from "@langfuse/browser";

const langfuse = new LangfuseBrowserClient({
  publicKey: "pk-lf-...",
  baseUrl: "https://cloud.langfuse.com", // 🇪🇺 EU region. 🇺🇸 US: https://us.cloud.langfuse.com 🇯🇵 Japan: https://jp.cloud.langfuse.com ⚕️ HIPAA: https://hipaa.cloud.langfuse.com
});

await langfuse.score({
  traceId: "trace-id",
  name: "user_feedback",
  value: 1,
});
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This package only supports score ingestion and uses public-key Bearer auth. Do not pass Langfuse secret keys to browser code. Configuration is passed via the constructor (browsers have no process.env); server-side packages read LANGFUSE_PUBLIC_KEY, LANGFUSE_SECRET_KEY, and LANGFUSE_BASE_URL environment variables instead.

Packages

Package	NPM	Description	Environments
@langfuse/tracing		OpenTelemetry-based tracing instrumentation	Node.js 20+
@langfuse/otel		LangfuseSpanProcessor to export OpenTelemetry spans to Langfuse	Node.js 20+
@langfuse/client		Prompt management, datasets, experiments, scores, full REST API	Universal JS
@langfuse/openai		observeOpenAI wrapper for tracing the OpenAI SDK	Universal JS
@langfuse/langchain		CallbackHandler for LangChain / LangGraph tracing	Universal JS
@langfuse/vercel-ai-sdk		Telemetry integration for Vercel AI SDK v7	Universal JS
@langfuse/browser		Browser score ingestion with public-key auth	Browser
@langfuse/core		Shared core: generated API client, logger, utilities	Universal JS

Documentation

• User feedback: https://langfuse.com/docs/observability/features/user-feedback
• Docs: https://langfuse.com/docs/observability/sdk/overview
• Reference: https://js.reference.langfuse.com
• LLM/agent-readable docs index: https://langfuse.com/llms.txt

License

MIT