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June 18, 2026

Score from the browser

Hassieb Pakzad

Use @langfuse/browser to send frontend feedback scores with only a public key.

Langfuse now ships @langfuse/browser for browser-side score ingestion. Use it to collect thumbs up/down feedback on chat responses, star ratings after generated content, or lightweight client-side quality signals and attach them directly to traces or observations.

The package is intentionally small: initialize LangfuseBrowserClient with your public key and call score(). It sends each score immediately via the ingestion API, so frontend interactions do not need batching or a flush lifecycle. Use @langfuse/client for backend services, scripts, CI jobs, and evaluation pipelines.

npm install @langfuse/browser

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

const langfuse = new LangfuseBrowserClient({
  publicKey: process.env.NEXT_PUBLIC_LANGFUSE_PUBLIC_KEY!,
  baseUrl: process.env.NEXT_PUBLIC_LANGFUSE_BASE_URL,
});

await langfuse.score({
  traceId: message.traceId,
  id: `user-feedback-${message.traceId}`,
  name: "user-feedback",
  value: 1,
  dataType: "BOOLEAN",
  comment: "Helpful answer",
});

Only expose the Langfuse public key in browser code. The secret key remains server-side only.

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