`sv` exposes a programmatic API for creating projects and running add-ons.

## `defineAddon`

Creates an add-on definition. See [create your own](community) for a full guide.

```js
import { transforms } from '@sveltejs/sv-utils';
import { defineAddon, defineAddonOptions } from 'sv';

export default defineAddon({
	id: 'my-addon',
	options: defineAddonOptions().build(),

	// called before run — declare dependencies and environment requirements
	setup: ({ dependsOn, unsupported, isKit }) => {
		if (!isKit) unsupported('Requires SvelteKit');
		dependsOn('eslint');
	},

	// the actual work — add files, edit files, declare dependencies
	run: ({ sv, options, cancel }) => {
		// add a dependency
		sv.devDependency('my-lib', '^1.0.0');

		// create or edit files using transforms from @sveltejs/sv-utils
		sv.file('src/lib/foo.ts', (content) => {
			return 'export const foo = true;';
		});

		sv.file(
			'src/routes/+page.svelte',
			transforms.svelte(({ ast, svelte }) => {
				svelte.addFragment(ast, '<p>Hello!</p>');
			})
		);

		// cancel at any point if something is wrong
		// cancel('reason');
	},

	// displayed after the add-on runs
	nextSteps: ({ options }) => ['Run `npm run dev` to get started']
});
```

The `sv` object in `run` provides `file`, `dependency`, `devDependency`, `execute`, and `pnpmBuildDependency`. For file transforms (AST-based editing of scripts, Svelte components, CSS, JSON, etc.), see [`@sveltejs/sv-utils`](sv-utils).

## `defineAddonOptions`

Builder for add-on options. Chained with `.add()` and finalized with `.build()`.

```js
import { defineAddonOptions } from 'sv';

const options = defineAddonOptions()
	.add('database', {
		question: 'Which database?',
		type: 'select',
		default: 'postgresql',
		options: [
			{ value: 'postgresql' },
			{ value: 'mysql' },
			{ value: 'sqlite' }
		]
	})
	.add('docker', {
		question: 'Add a docker-compose file?',
		type: 'boolean',
		default: false,
		// only ask when database is not sqlite
		condition: (opts) => opts.database !== 'sqlite'
	})
	.build();
```

Options are asked in order. The `condition` callback receives the answers collected so far — return `false` to skip the question (its value will be `undefined`).

## `create`

Programmatically create a new Svelte project.

```js
import { create } from 'sv';

create('./my-app', {
	name: 'my-app',
	template: 'minimal',
	types: 'typescript'
});
```

## `add`

Programmatically run add-ons against an existing project.

```js
import { add, officialAddons } from 'sv';

await add({
	cwd: './my-app',
	addons: { prettier: officialAddons.prettier },
	options: { prettier: {} },
	packageManager: 'npm'
});
```