Langfuse

Langfuse is an open-source LLM engineering platform providing traces, evaluations, prompt management, and cost analytics for production AI applications. We rate it 85/100 — an outstanding choice for any team building with LLMs who needs deep visibility into model behavior, costs, and quality without vendor lock-in.

What is Langfuse?

Founded in 2022 by Maximilian Deichmann, Marc Klingen, and Clemens Rawert — alumni of Y Combinator's W23 batch — Langfuse was born just as GPT-4 was released, directly addressing the void in LLM observability tooling. The Berlin-based team built what has become the most widely-deployed open-source solution in the LLMOps space: 24,600+ GitHub stars, 26M+ SDK installs per month, and adoption across 63 Fortune 500 companies by early 2026.

In January 2026, Langfuse was acquired by ClickHouse as part of a $400M Series D round that tripled ClickHouse's valuation to $15B. The platform remains 100% open-source under the MIT license, and Langfuse Cloud continues operating as a standalone service. The acquisition strengthens Langfuse's long-term infrastructure — Langfuse Cloud has always been built entirely on ClickHouse under the hood.

Key Features of Langfuse

• LLM Tracing & Observability: Instrument any LLM call, retrieval step, embedding, or tool execution with nested span capture. The UI lets you replay exact inputs/outputs, inspect latency at each step, and drill into token usage. Supports complex architectures including agents, RAG pipelines, and multi-step chains.
• Prompt Management: Centralized version control and collaborative iteration on prompts with server-side and client-side caching. Change a prompt in production without redeploying your application, and A/B test variants against real traffic.
• Evaluations (LLM-as-a-Judge + Human): Run automated evals using configurable LLM judges, collect user feedback (thumbs up/down, ratings) via SDK, trigger manual labeling workflows, and define custom eval pipelines via the API. Evaluation scores are linked directly to traces for drill-down analysis.
• Datasets & Testing: Build test sets from production traces, run offline evals before deploying, and track regression across model versions or prompt changes over time.
• Cost & Latency Analytics: Break down LLM spend by user, feature, session, or model. Track P50/P95/P99 latencies. Identify which parts of your pipeline are slow or expensive with a single click.
• LLM Playground: Jump directly from any trace into the playground to reproduce and iterate on a specific prompt-response pair. Supports side-by-side model comparison.

What Users Say About Langfuse

Sentiment across Reddit, Hacker News, and Product Hunt is overwhelmingly positive, with Langfuse consistently called "the observability tool the LLM space actually needed." On Hacker News, the Launch HN thread drew praise specifically for the self-hosting story: "Finally something I can run in my own infra without a per-seat license that costs more than my model inference bill." A recurring theme in Reddit's r/MachineLearning and r/LangChain is that Langfuse is the only tool that makes agent debugging tractable — the nested trace view for multi-step chains is cited as a genuine differentiator over alternatives like LangSmith.

The most common complaint is that the free Cloud tier's 30-day data retention is limiting for teams that want longer-term trend analysis without immediately upgrading. Some self-hosters also note that initial Kubernetes deployment requires some ClickHouse configuration knowledge. That said, reviewers consistently praise the speed of the team in responding to issues and shipping features.

Langfuse Pricing

Langfuse Cloud uses a usage-based freemium model. The free tier is genuinely useful — 50,000 events/month with 2 users is substantially more generous than most competitors. Paid tiers scale on event volume and unlock longer data retention and compliance features rather than gating core functionality. Self-hosting is always free under the MIT license.

Plan	Price	Key Limits
Hobby (Free)	$0/month	50,000 events/mo, 2 users, 30-day retention
Pro	$29/month	100,000 events/mo, unlimited users, 90-day retention; +$8/mo per additional 100k events
Team	Contact	Custom event volume, SSO, SAML, SLA, priority support
Self-Hosted	Free	MIT license, unlimited events, full feature set, runs on ClickHouse

Who Should Use Langfuse?

Best for: ML engineers and full-stack developers shipping production LLM applications — especially those building RAG systems, agents, or multi-step pipelines where tracing individual components is critical. Teams that are cost-conscious and want observability without per-seat pricing will find the unlimited-user model across all paid plans highly attractive. Companies with strict data residency requirements will appreciate the robust self-hosting story.

Not ideal for: Teams that only call a single LLM endpoint with no orchestration — simpler tools like basic logging may suffice. Enterprises needing fully on-prem deployment with dedicated support may want to evaluate the Team tier carefully before committing.

Pros and Cons

Pros:

• 100% open-source (MIT) with a best-in-class self-hosting story — Docker Compose to Kubernetes in under 30 minutes
• Unlimited users on all paid tiers — no per-seat pricing surprises
• Native integrations with LangChain, LlamaIndex, OpenAI SDK, LiteLLM, Haystack, and more
• Active development: 6,700+ commits, 24.6k GitHub stars, and the team ships features weekly
• Now backed by ClickHouse infrastructure expertise — strong long-term durability signal

Cons:

• Free tier's 30-day data retention limits historical trend analysis for cost-sensitive teams
• Self-hosted setup requires familiarity with ClickHouse configuration for optimal performance at scale
• No native mobile monitoring dashboard — observability is web-only

Alternatives to Langfuse

LangSmith (by LangChain) is the most direct competitor — tighter LangChain integration but closed-source, per-seat pricing, and no self-hosting option. Helicone is a lighter-weight alternative focused purely on OpenAI API logging with a simpler setup, but lacks Langfuse's eval framework and prompt management depth. Arize Phoenix is a strong open-source option for ML teams already in the Arize ecosystem, with particularly good support for multimodal and embedding observability.

Verdict: Is Langfuse Worth It?

Langfuse is the best observability platform for LLM applications available today, full stop. The combination of deep tracing, a production-grade eval framework, prompt versioning, and cost analytics — all in a single open-source tool that you can self-host for free — is unmatched. The ClickHouse acquisition adds long-term infrastructure confidence. We rate it 85/100: the minor deductions are for the restrictive free-tier retention window and the ClickHouse knowledge prerequisite for large-scale self-hosting. For any team shipping production AI, Langfuse should be the first tool you instrument.

Frequently Asked Questions

Is Langfuse free?

Yes. Langfuse has a free Hobby plan on Cloud (50,000 events/month, 2 users, 30-day retention) and is completely free to self-host under the MIT license with no event or user limits.

What platforms does Langfuse support?

Langfuse is a web-based platform. SDKs are available for Python and JavaScript/TypeScript. It integrates natively with LangChain, LlamaIndex, OpenAI SDK, LiteLLM, Haystack, DSPy, Instructor, AutoGen, and Ollama, among others.

How does Langfuse compare to LangSmith?

LangSmith is closed-source and priced per seat, while Langfuse is MIT-licensed with unlimited users on paid plans and a full self-hosting option. Langfuse has a more comprehensive eval framework; LangSmith has tighter native LangChain integration. For teams not locked into LangChain, Langfuse is generally the better choice.

Is Langfuse open source?

Yes. Langfuse's core is MIT-licensed and available at github.com/langfuse/langfuse with 24,600+ stars. The self-hosted version has full feature parity with the Cloud offering.

What happened after ClickHouse acquired Langfuse?

ClickHouse acquired Langfuse in January 2026 as part of its $400M Series D. The product remains open-source under the MIT license, Langfuse Cloud continues as a standalone service, and the team's roadmap is unchanged. The acquisition aligns strategically since Langfuse's architecture is built entirely on ClickHouse.