Getting started

Install

npm

npm i -D genever

pnpm

pnpm add -D genever

yarn

yarn add -D genever

TIP

genever requires Node.js 24 or later. Its output is plain TypeScript, so it is a dev dependency only.

Generate types

npx genever schemas/user.json --name User

genever writes schemas/user.ts next to the schema (or -o to choose the path), and prints the file it wrote:

• The root schema becomes the type named by --name (Schema by default).
• Every definition in the root $defs (or draft 7 definitions) becomes an exported type named after its key, in PascalCase, whether or not it is referenced.
• A schema referenced by $ref from anywhere else in the document becomes a named type too, named after its key in any nested $defs, or else after its path. Everything else is inlined.

// Generated by genever. Do not edit by hand, regenerate it instead.

export type User = {
    id: `usr_${string}`;
    home?: Address;
};

export type Address = {
    city: string;
};

The file is formatted with your project's Biome or Prettier config, if either is installed.

If the schema has a mistake, such as a misspelled keyword, genever fails with a JSON Pointer to it instead of writing a looser type. See Strict mode.

Check types in CI

Commit the generated file, and check it is up to date in CI:

npx genever schemas/user.json --name User --ci

--ci generates the types without writing, and fails if the file would change. It is on by default when genever detects CI (with ci-info), so the same command writes locally and checks in CI.

In an Nx workspace, a cached target per schema does that before compiling:

// project.json
{
    "targets": {
        "genever": {
            "executor": "nx:run-commands",
            "options": {
                "command": "genever schemas/user.json --name User",
                "cwd": "{projectRoot}"
            },
            "cache": true,
            "inputs": ["{projectRoot}/schemas/user.json"],
            "outputs": ["{projectRoot}/schemas/user.ts"]
        }
    }
}

Next steps

• Type mapping: how each keyword becomes a type.
• Strict mode: the mistakes genever rejects, and what it generates without strict mode.
• OpenAPI documents: types for every schema of a spec.
• Juniper round trip: getting Juniper's types back from its JSON.
• API and CLI reference: every option, and running genever from code.