oasis-gen reads an OpenAPI document and writes one dependency-free TypeScript file, with types for every operation and a small fetch-based runtime.

• OpenAPI 3.2: QUERY operations, sequential media types (JSON Lines, server-sent events), multi-file documents, and JSON Schema 2020-12. OpenAPI 3.0 and 3.1 documents are accepted too.
• Strict types: status narrows data to the declared response. Statuses that the document does not declare stay in the type. Request types respect readOnly and writeOnly.
• Zero runtime dependencies: the output runs anywhere fetch is available. There is no runtime package to install and nothing to configure.

Example

npx oasis-gen openapi.yaml -o src/api.ts

import { createClient } from "./api.ts";

const api = createClient({ baseUrl: "https://api.example.com" });

const res = await api.GET("/pets/{petId}", { path: { petId: 1 } });
if (res.status === 200) {
  res.data.name; // typed from the 200 response
} else if (res.status === 404) {
  res.data.title; // typed from the 404 response
}

Install

npm install --save-dev oasis-gen

The CLI and the generated client need Node.js 22 or later. The client also runs in browsers (tested in Chromium, Firefox, and WebKit) and Bun, and type-checks with TypeScript 5.0 or later. Generate only from documents you trust: oasis-gen reads any local file that a $ref points to.

The package ships prebuilt binaries for macOS, Linux, and Windows, on arm64 and x64. npm installs only the one for your platform. Archives are also attached to each GitHub release. To build from source instead:

cargo install --git https://github.com/22mb/oasis

Documentation

• Getting started: from an OpenAPI document to a typed API call
• Strict types: the rules that the generated types follow
• Calling operations, Middleware, and Authentication
• Recipes: common tasks and troubleshooting
• CLI and API, Schemas, and OpenAPI support

Changes in each release are listed in CHANGELOG.md.

Contributing

See CONTRIBUTING.md for the development setup and the design of the generator.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.