Langfuse
Open-source LLM observability platform — traces, evaluates, and monitors LLM applications with a REST API, Python/JS SDKs, and native OpenAI/LangChain/CrewAI integrations.
Score Breakdown
⚙ Agent Friendliness
🔒 Security
HTTPS enforced. Key pairs are project-scoped. Self-hosted gives full data control — no data leaves your infrastructure. SOC 2 Type II for cloud. EU data residency available.
⚡ Reliability
Best When
You're building or debugging an LLM agent pipeline and need to trace every call, track costs, and evaluate output quality systematically.
Avoid When
You only need simple logging — Langfuse adds overhead and complexity that may not be worth it for simple single-call LLM apps.
Use Cases
- • Tracing every LLM call in an agent pipeline with cost, latency, and token tracking
- • Running automated evaluations on agent outputs (LLM-as-judge, heuristic, human annotation)
- • Prompt versioning and A/B testing with the Prompt Management API
- • Monitoring agent runs in production for quality regression
- • Debugging failing agent chains by inspecting individual span traces
Not For
- • Infrastructure-level monitoring (use Datadog or Prometheus for server metrics)
- • Real-time alerting on production errors (better handled by Sentry or PagerDuty)
- • Non-LLM applications (purpose-built for language model observability)
Interface
Authentication
Public key + Secret key pair per project. Sent as Basic Auth headers. Keys are project-scoped but not operation-scoped within a project.
Pricing
Self-hosted is MIT licensed and completely free. Cloud free tier is genuinely useful for small projects.
Agent Metadata
Known Gotchas
- ⚠ Async SDK flush required before process exit — missing this loses the last traces
- ⚠ Batch ingestion is eventually consistent — don't query traces immediately after writing
- ⚠ Nesting traces correctly requires explicit parent observation IDs — easy to create flat traces accidentally
- ⚠ Prompt management prompts are cached client-side — updates take time to propagate
- ⚠ Self-hosted requires Postgres + ClickHouse for full features (ClickHouse is heavy)
Alternatives
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Scores are editorial opinions as of 2026-03-07.