synopkg/site/src/faq/only-allow-types-in-dev-dependencies.mdx

Consistent dependency versions in large JavaScript Monorepos

---
title: Only allow @types packages in devDependencies
---

Only allow TypeScript [@types](HREF_TYPES) packages from being used anywhere other than in the `devDependencies` section of package.json.

### 1. Add a version group

- Match all **dependencies** whose name starts with `@types/`.
- Only match those dependencies when they appear anywhere **except** `devDependencies`.
- Define the behaviour of this group as **isBanned**.
- Add a **label** to document the decision/expectation.

```json title=".synopkgrc.json"
{
  "versionGroups": [
    {
      "dependencies": ["@types/**"],
      "dependencyTypes": ["!dev"],
      "isBanned": true,
      "label": "@types packages should only be under devDependencies"
    }
  ]
}
```

### 2. Look for mismatches

Any `@types` packages which are in the wrong location can then be found and manually moved:

```bash
synopkg list-mismatches
```