Every option in the catalog for when you need to trace, score and debug what your AI app actually did — 12 LLM evaluation and observability tools, 12 of them free or freemium, with the pricing tier printed on every row.
Flocci AI Tools lists 12 of them, ordered free tiers first: Arize Phoenix, Google Stax, Laminar, DeepEval and EleutherAI LM Evaluation Harness. Every one of them is free or has a free tier. Each entry states what it uniquely does rather than a score.
6 on this page are marked fully free with no paid plan at all: Arize Phoenix, Google Stax, Laminar, DeepEval and EleutherAI LM Evaluation Harness. The remaining 6 are freemium, trial or paid, and each is labelled with its exact tier so nothing surprises you at sign-up.
Free tools first, then freemium, then trial, then paid, and alphabetically inside each tier. Nobody pays to appear higher: Flocci AI Tools carries no ads, no sponsored slots and no paid listings, so the order reflects price and nothing else.
Arize Phoenix, Google Stax, Laminar, Braintrust and Langfuse all work in a browser tab with no install needed — just open the site and go. 9 of the 12 free LLM evaluation and observability tools listed here are browser-based.
Google Stax and Langfuse support Google sign-in, so you can start without creating a new account. That's 2 of the 12 free LLM evaluation and observability tools on this page.
DeepEval, EleutherAI LM Evaluation Harness and OpenLLMetry (Traceloop) can be self-hosted or run locally without a browser — useful for privacy, air-gapped networks, or avoiding API rate limits. 3 of the 12 free LLM evaluation and observability tools here run offline.
| Tool | Pricing | Type | Listed for |
|---|---|---|---|
| Arize Phoenix | Free | LLM Eval & Observability | Fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported) |
| Google Stax | Free | LLM Eval & Observability | Build evals with human raters or LLM autoraters on your own data |
| Laminar | Free | LLM Eval & Observability | Open-source observability and evals platform for AI agents (Apache-2.0) |
| DeepEval | Free | LLM Eval & Observability | Open-source LLM evaluation framework with pytest-style tests and 50+ metrics |
| EleutherAI LM Evaluation Harness | Free | LLM Eval & Observability | Standard open framework for running hundreds of benchmarks (MMLU, GSM8K and more) against any LLM |
| OpenLLMetry (Traceloop) | Free | LLM Eval & Observability | OpenTelemetry-based instrumentation for LLM calls, vector DBs and frameworks |
| Braintrust | Freemium | LLM Eval & Observability | Free Starter plan ships model credits and scored evals with no card required |
| Langfuse | Freemium | LLM Eval & Observability | Fully open-source and self-hostable for free via Docker Compose/Kubernetes, not just a hosted SaaS |
| LangSmith | Freemium | LLM Eval & Observability | Tracing, evaluation datasets and prompt playground for LLM apps and agents |
| Opik (Comet) | Freemium | LLM Eval & Observability | Open-source LLM tracing, evaluation and prompt-optimization platform (Apache-2.0) |
| Promptfoo | Freemium | LLM Eval & Observability | Open-source CLI/library for evaluating prompts, models and RAG pipelines side by side, runs in CI |
| W&B Weave | Freemium | LLM Eval & Observability | Agent-native tracing model with sessions, steps, tools and sub-agents as first-class concepts (not generic spans) |