LLM Eval & ObservabilityfreemiumNew

Opik (Comet)

Open-source LLM tracing, evaluation and prompt-optimization platform (Apache-2.0)

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What Opik (Comet) does

  • Open-source LLM tracing, evaluation and prompt-optimization platform (Apache-2.0)
  • Free cloud plan with 25k spans a month, up to 10 team members and 60-day retention
  • Self-host with no limits

Opik (Comet) — straight answers

What is Opik (Comet)?

Opik (Comet) is listed under LLM Eval & Observability, in the AI Models & Local Execution category on Flocci AI Tools. Open-source LLM tracing, evaluation and prompt-optimization platform (Apache-2.0). It is freemium — a usable free tier with paid plans above it, and it lives at comet.com.

Is Opik (Comet) free?

Opik (Comet) is freemium: there is a free tier you can work in and paid plans above it. It is one of 404 freemium tools in the catalog, all labelled the same way so you are never surprised by a paywall.

What can Opik (Comet) do?

Opik (Comet) does 3 things the catalog singles out: Open-source llm tracing, evaluation and prompt-optimization platform (apache-2.0); free cloud plan with 25k spans a month, up to 10 team members and 60-day retention; self-host with no limits.

What is the best free alternative to Opik (Comet)?

Arize Phoenix is the closest free alternative: it sits in the same LLM Eval & Observability sub-category and is free. DeepEval, EleutherAI LM Evaluation Harness and Google Stax also start free. The full list is on the alternatives page.

See the full list →

Opik (Comet) alternatives

Compare all alternatives →

Langfuse

LLM Eval & Observability
freemium
  • Fully open-source and self-hostable for free via Docker Compose/Kubernetes, not just a hosted SaaS
  • Hobby cloud plan is free with no credit card, 50k observability units/month
  • Combines tracing, prompt management, evals and datasets in one open platform
Visit

Braintrust

LLM Eval & Observability
freemium
  • Free Starter plan ships model credits and scored evals with no card required
  • Unlimited users/projects/datasets/playgrounds even on the free tier
  • Built-in playground for side-by-side prompt/model comparison against production traces
Visit

Promptfoo

LLM Eval & Observability
freemium
  • Open-source CLI/library for evaluating prompts, models and RAG pipelines side by side, runs in CI
  • Automated red-teaming to surface prompt injection, jailbreak and data-leak vulnerabilities
  • 300,000+ user community with an enterprise tier for teams needing hosted guardrails
Visit

W&B Weave

LLM Eval & Observability
freemium
  • Agent-native tracing model with sessions, steps, tools and sub-agents as first-class concepts (not generic spans)
  • Pre-built safety/quality scorers for toxicity, bias, PII and hallucination detection out of the box
  • Built on Weights & Biases' existing ML-experiment infrastructure, useful for teams already on W&B
Visit

Arize Phoenix

LLM Eval & Observability
free
  • Fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported)
  • Combines tracing, evals, datasets, experiments and prompt playground in one local-first tool
  • AI engineering agent (PXI) built in for automated troubleshooting of traces
Visit

Google Stax

LLM Eval & Observability
freeNew
  • Build evals with human raters or LLM autoraters on your own data
  • Compare models and prompts on quality, latency and token cost
  • Prebuilt and custom evaluators
Visit

Head-to-head comparisons

Opik (Comet) vs LangfuseOpik (Comet) vs BraintrustOpik (Comet) vs PromptfooOpik (Comet) vs W&B WeaveOpik (Comet) vs Arize PhoenixOpik (Comet) vs Google Stax