Honest, side-by-side comparisons. We show where each alternative wins and where Spanlens does. Real tradeoffs without marketing fog.
The most mature OSS LLM observability tool. We diverge on instrumentation model (proxy vs SDK), license boundary (full MIT vs OSS + EE folder), and built-in eval shape.
The closest architectural match. Both are proxy-based, though Helicone entered maintenance mode after its 2026 Mintlify acquisition. We add Critical Path agent tracing, Prompt A/B with Welch t-test, and tighter logging durability with ClickHouse fallback.
LangChain's commercial offering. Excellent if you live inside LangChain, locked-in if you don't. Spanlens is framework-agnostic.
Eval-first, closed-source SaaS. Strong eval UX. We bundle eval into a full observability platform that you can self-host with one Docker command.
Source-available (ELv2) observability from Arize. Python-first, ML-engineer-leaning. Spanlens is built for the application developer running LLM calls in production.
We'll write a comparison for any LLM observability tool that has at least a public docs page. Email support@spanlens.io and we'll add it.