LLM observability
Tracing, evals and cost tracking for LLM apps. 10 vendors tracked, 9 with a verified free tier.
Langfuse
Langfuse Hobby lists 50k units/month with all platform features (limited) and no card — the broadest verified free LLM tier. Helicone Hobby (10,000 requests, 1 GB) is simpler for gateway-style logging. Arize AX Free (25k spans, 1 GB/mo, no card) and Opik Free Cloud (25k spans/mo) are solid runners-up; LangSmith Developer caps you at 1 seat and 5k base traces, and Lunary now requires payment for new workspaces.
Based only on the plan limits recorded below; limits change — check sources.
All LLM observability vendors
Arize AX / Phoenix
Free tier25k spans/mo; 1 GB/mo; 10 issues/mo; no card. Phoenix is open source
Braintrust
Free tier$0/month; $10 credits; free usage for traces, evals and whole team; no card
Helicone
Free tier10,000 free requests; 1 GB storage; 1 seat
Laminar
Free tier$0/month
Langfuse
Free tier50k units/mo; all platform features with limits; no card
LangSmith
Free tier$0/seat; up to 5k base traces/mo; 1 seat
Opik (Comet)
Free tierCloud: 25k spans/month. Open source: $0
Portkey
Free tier10k recorded logs/month
W&B Weave
Free tier$0/mo; Weave ingestion 1 GB/mo
Lunary
No free tierNo new free workspaces: payment required to activate cloud workspace
Get the LLM observability watchlist weekly
When any of these 10 vendors changes a free tier or price, you’ll hear first.