Kiln AI

Open-source workbench for building, evaluating, and fine-tuning AI agents across 190+ models.

Freemium· Free Individual tier; Team (request access); Enterprise (custom)EvaluationMulti-model

Best for

Pick Kiln AI if you want a local-first, Git-friendly workbench to evaluate and fine-tune LLM agents without piping prompts and datasets into a SaaS.

Skip if

Skip it if you want a fully-hosted, browser-based eval platform for non-technical teammates who won't install a desktop app.

Kiln AI is a desktop workbench plus open-source Python library for teams building production AI systems. It bundles the loop you'd otherwise stitch together yourself: RAG, tools/MCP, sub-agents, LLM-as-judge evals with golden datasets, synthetic data generation, prompt and agent auto-optimization, and fine-tuning. The desktop app runs locally on macOS, Windows, and Linux, with datasets versioned in Git so engineers, data scientists, and PMs can collaborate on the same eval set without a SaaS lock-in.

What sets Kiln apart is the split between a genuinely free, MIT-licensed Python library (4,500+ GitHub stars) for production deployment and a paid Kiln Pro layer that adds an AI assistant, auto-generated evals, and optimization. It supports 190+ models across OpenAI, Anthropic, Gemini, Ollama, Bedrock, and Azure OpenAI, so you're not locked to one provider. The Individual tier is free with rate-limited Pro features; Team is request-access with higher limits and email support; Enterprise adds SSO/SAML, SLAs, and a solutions engineer.

It's best thought of as a serious alternative to hosted eval/agent platforms like Braintrust or LangSmith for teams that want a local-first, Git-friendly workflow and don't want their prompts and datasets sitting in someone else's cloud.

Editor's take

Kiln nails an underserved niche: a credible open-source rival to Braintrust and LangSmith that keeps your eval data on your laptop and in Git. The free Python library is the real product; Kiln Pro is the sweetener. For serious agent teams that care about data sovereignty, it's one of the more honest tools in this space.

— The AI Tool Bible editorial team

Pros

✅ MIT-licensed Python library with 4,500+ GitHub stars
✅ Local-first desktop app with Git-versioned datasets
✅ Supports 190+ models across OpenAI, Anthropic, Gemini, Ollama, Bedrock
✅ Covers build, eval, and fine-tune in one workbench
✅ Genuine free tier, not a time-limited trial

Cons

⚠️ Best Pro features (auto-optimization, AI assistant) are rate-limited on free tier
⚠️ Team tier is request-access, not self-serve
⚠️ Desktop-first means it's less collaborative than fully-hosted eval platforms