Best free Google Stax alternatives

Looking for a free alternative to Google Stax? Here are 9 llm eval & observability worth trying — 9 with a free tier. Google Stax itself is free.

ToolGoogle Stax (you searched)Arize PhoenixDeepEvalEleutherAI LM Evaluation Harness
Pricingfreefreefreefree
Best forBuild evals with human raters or LLM autoraters on your own dataFully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported)Open-source LLM evaluation framework with pytest-style tests and 50+ metricsStandard open framework for running hundreds of benchmarks (MMLU, GSM8K and more) against any LLM
VisitOpen ↗Open ↗Open ↗Open ↗

Google Stax alternatives — straight answers

What is the best free alternative to Google Stax?

Arize Phoenix is the closest free alternative to Google Stax: same LLM Eval & Observability sub-category, and it is free. Fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported)

Are there free Google Stax alternatives?

Yes — 9 of the 9 alternatives listed here are free or freemium: Arize Phoenix, DeepEval, EleutherAI LM Evaluation Harness, OpenLLMetry (Traceloop), Laminar. None of them are paid-only.

Is Google Stax free?

Google Stax is free. There is no paid plan attached to it in the catalog.

How were these Google Stax alternatives chosen?

They are the other tools in LLM Eval & Observability, then the rest of AI Models & Local Execution, ordered free tiers first and capped at 9. There is no sponsorship and no paid placement in that ordering — only the pricing tier decides.

All Google Stax alternatives

Browse LLM Eval & Observability →

Arize Phoenix

LLM Eval & Observability
free

✦ WhyA Google Stax alternative — Fully open-source, self-hostable with zero setup via `uvx` (pip/conda also supported).

  • 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

DeepEval

LLM Eval & Observability
freeNew

✦ WhyA Google Stax alternative — Open-source LLM evaluation framework with pytest-style tests and 50+ metrics.

  • 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
Visit

EleutherAI LM Evaluation Harness

LLM Eval & Observability
freeNew

✦ WhyA Google Stax alternative — Standard open framework for running hundreds of benchmarks (MMLU, GSM8K and more) against any LLM.

  • Standard open framework for running hundreds of benchmarks (MMLU, GSM8K and more) against any LLM
  • Backs the Hugging Face Open LLM evaluations
  • MIT licensed CLI and Python library
Visit

OpenLLMetry (Traceloop)

LLM Eval & Observability
freeNew

✦ WhyA Google Stax alternative — OpenTelemetry-based instrumentation for LLM calls, vector DBs and frameworks.

  • OpenTelemetry-based instrumentation for LLM calls, vector DBs and frameworks
  • Ships traces to Datadog, Grafana, Honeycomb or any OTel backend
  • Apache-2.0
Visit

Laminar

LLM Eval & Observability
freeNew

✦ WhyA Google Stax alternative — Open-source observability and evals platform for AI agents (Apache-2.0).

  • Open-source observability and evals platform for AI agents (Apache-2.0)
  • Traces, session replay for browser agents and evaluations
  • Self-hostable
Visit

Langfuse

LLM Eval & Observability
freemium

✦ WhyA Google Stax alternative — Fully open-source and self-hostable for free via Docker Compose/Kubernetes, not just a hosted SaaS.

  • 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

✦ WhyA Google Stax alternative — Free Starter plan ships model credits and scored evals with no card required.

  • 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

✦ WhyA Google Stax alternative — Open-source CLI/library for evaluating prompts, models and RAG pipelines side by side, runs in CI.

  • 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

✦ WhyA Google Stax alternative — Agent-native tracing model with sessions, steps, tools and sub-agents as first-class concepts (not generic spans).

  • 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

Google Stax head-to-head

Google Stax vs Arize PhoenixGoogle Stax vs DeepEvalGoogle Stax vs EleutherAI LM Evaluation HarnessGoogle Stax vs OpenLLMetry (Traceloop)Google Stax vs LaminarGoogle Stax vs LangfuseGoogle Stax vs BraintrustGoogle Stax vs Promptfoo