@langfuse/core

@langfuse/core

Langfuse is the open-source LLM engineering platform: tracing & evaluation for AI and agent applications, prompt management, datasets & experiments, and evaluation (scores). This is the shared core package of the Langfuse JS SDK: the generated REST API client (LangfuseAPIClient), logger, environment-variable handling, media types, and the propagateAttributes context propagation utilities. Use @langfuse/tracing + @langfuse/otel for tracing and @langfuse/client for prompt management, datasets/experiments, and scores.

This is the current SDK generation (@langfuse/* scoped packages). The unscoped langfuse-core npm package belongs to the legacy v3 SDK. Migration guides: v3 → v4, v4 → v5.

Environment variables

Configuration shared across all @langfuse/* packages:

LANGFUSE_PUBLIC_KEY="pk-lf-..."
LANGFUSE_SECRET_KEY="sk-lf-..."
LANGFUSE_BASE_URL="https://cloud.langfuse.com" # 🇪🇺 EU region. 🇺🇸 US: https://us.cloud.langfuse.com, 🇯🇵 Japan: https://jp.cloud.langfuse.com, ⚕️ HIPAA: https://hipaa.cloud.langfuse.com

Packages

Package	NPM	Description	Environments
@langfuse/tracing		OpenTelemetry-based tracing instrumentation	Node.js 22+
@langfuse/otel		LangfuseSpanProcessor to export OpenTelemetry spans to Langfuse	Node.js 22+
@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

• 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