LAPIS (Lightweight API Specification for Intelligent Systems) is an API specification format designed for LLMs, not for code generators.
OpenAPI works fine for documentation tools. When an LLM processes it, it spends tokens on information the model doesn’t need. LAPIS cuts that overhead: 85.5% fewer tokens than OpenAPI YAML, 88.6% fewer than JSON, measured on real APIs from GitHub, Twilio and DigitalOcean.
It also includes centralized error handling, webhook triggers, rate limiting descriptions and operation flows. Converts automatically from OpenAPI 3.x. Published as an open specification under CC BY 4.0.
Paper on arXiv: arxiv.org/abs/2602.18541.
+12 stars on GitHub.