LLM Eval & Observabilityfreemium

W&B Weave

Agent-native tracing model with sessions, steps, tools and sub-agents as first-class concepts (not generic spans)

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What W&B Weave does

  • 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

W&B Weave — straight answers

What is W&B Weave?

W&B Weave is listed under LLM Eval & Observability, in the AI Models & Local Execution category on Flocci AI Tools. Agent-native tracing model with sessions, steps, tools and sub-agents as first-class concepts (not generic spans). It is freemium — a usable free tier with paid plans above it, and it lives at wandb.ai.

Is W&B Weave free?

W&B Weave 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 W&B Weave do?

W&B Weave does 3 things the catalog singles out: 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.

What is the best free alternative to W&B Weave?

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 →

W&B Weave 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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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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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
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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

W&B Weave vs LangfuseW&B Weave vs BraintrustW&B Weave vs PromptfooW&B Weave vs Arize PhoenixW&B Weave vs Google StaxW&B Weave vs DeepEval