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README.md	README.md
package.json	package.json
tsconfig.json	tsconfig.json
tsup.config.ts	tsup.config.ts
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@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

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,
});

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	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