Spanlight: open-source LLM observability that runs on a single Postgres
Cold-Conclusion-6511 · reddit · 2026-10-20
A solo developer released Spanlight, an MIT-licensed open-source LLM observability tool: one Docker image plus one Postgres, fully self-hostable.
- Tracing: logs every LLM call (prompt, reply, latency, tokens, cost, errors) grouped into traces and sessions, with search and side-by-side trace comparison
- Cost: versioned price table, per-call breakdown, daily reconciliation against Anthropic/OpenAI bills, budgets that alert or soft-block gateway calls
- The Doctor: 15 fixed non-LLM rules flag retry storms, ignored Retry-After, truncated outputs, tool loops, cost/latency spikes — each with evidence and a suggested fix
- Optional gateway: retries, fallbacks, per-key rate limits and caching via baseurl swap; an Integration Lab simulates provider failures
The author used Claude Code heavily but designs, reviews and tests every change; the backend has 4,121 tests against real Postgres. Fresh clone to first stored trace took 59 seconds.
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