Haeseong Jeon

Haeseong Jeon

Building open-source LLM observability
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About

I'm Haeseong, founder of Spanlens, an open-source LLM observability platform for developers shipping AI products. Spanlens lets you monitor costs, latency, and traces across OpenAI, Anthropic, Gemini, and more with just two lines of code. Self-hostable, MIT licensed, and built because production LLM costs are invisible until they hurt. Launching on Product Hunt June 3. Always happy to connect with builders and the PH community.

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Maker History

  • Spanlens
    SpanlensOpen-source LLM observability in one line of code
    Jun 2026
    • 🎉
    Joined Product HuntDecember 21st, 2025

Forums

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1mo ago

Spanlens - Open-source LLM observability in one line of code

Spanlens records every OpenAI, Anthropic, Gemini, Azure, and Ollama call with one line of code. Get cost, latency, agent traces with Critical Path, anomaly alerts, PII scan, and model-swap suggestions out of the box. MIT, self-hostable, free tier that doesn't punish growth.
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2mo ago

We built an open-source LLM observability tool. Would love your feedback!

Hey Product Hunt community!

I'm Haeseong, the solo founder behind Spanlens. I built it because I kept seeing the same problem around me. Developers shipping AI products had no clear picture of what was actually happening with their LLM calls in production. Costs were invisible, errors were silent, and when something broke, there was no trace.

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