LAPIS

LAPIS (Lightweight API Specification for Intelligent Systems) is an API specification format designed for LLMs to read.

OpenAPI works fine for documenting and generating code. But when an LLM reads it, it spends tokens on information the model doesn’t need. LAPIS cuts that out: 85.5% fewer tokens than OpenAPI YAML, 88.6% fewer than JSON, measured on real APIs from GitHub, Twilio and DigitalOcean.

It also has centralized error handling, webhook triggers, rate limiting descriptions and operation flows. It converts automatically from OpenAPI 3.x and the specification is open, under CC BY 4.0.

Paper on arXiv: arxiv.org/abs/2602.18541.

+12 stars on GitHub.