Honest, side-by-side comparisons. We show where each alternative wins and where Spanlens does. Real tradeoffs without marketing fog.
Want the whole field first? Twelve tools with stars, licence, and development activity.
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 a log queue that replays failed writes.
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.
Apache 2.0 with nothing held back, so the licence argument does not apply. Opik organises around evaluation and instruments through the SDK. Spanlens organises around cost and captures existing calls through the proxy.
The closest architecture after Helicone: both sit in front of the provider. Portkey open-sources the gateway and sells the observability, while Spanlens ships both halves under MIT.
Different jobs rather than rivals. LiteLLM routes across a hundred providers and hands logging to a backend; Spanlens is a backend of that kind. Many teams run both.
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.