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Google Stax

Build evals with human raters or LLM autoraters on your own data

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What Google Stax does

  • 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

Google Stax — straight answers

What is Google Stax?

Google Stax is listed under LLM Eval & Observability, in the AI Models & Local Execution category on Flocci AI Tools. Build evals with human raters or LLM autoraters on your own data. It is free, with no paid plan attached, and it lives at stax.withgoogle.com.

Is Google Stax free?

Google Stax is listed as fully free — there is no paid tier attached to it in the catalog. That makes it one of the 399 entries on Flocci AI Tools with no upgrade path built in.

What can Google Stax do?

Google Stax does 3 things the catalog singles out: 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.

What is the best free alternative to Google Stax?

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 Laminar also start free. The full list is on the alternatives page.

See the full list →

Google Stax 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
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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
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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
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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
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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
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DeepEval

LLM Eval & Observability
freeNew
  • Open-source LLM evaluation framework with pytest-style tests and 50+ metrics
  • RAG, agent and conversational metrics; red-teaming module
  • Apache-2.0; optional Confident AI cloud has a free tier
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Head-to-head comparisons

Google Stax vs LangfuseGoogle Stax vs BraintrustGoogle Stax vs PromptfooGoogle Stax vs W&B WeaveGoogle Stax vs Arize PhoenixGoogle Stax vs DeepEval