How to fix npm WARN publish npm WARN publish No license field in npm

Select a license based on your project type:

Permissive licenses (best for broad adoption):
- MIT: Most popular for npm packages. Simple, allows commercial use.
- Apache-2.0: Includes patent protection.
- ISC: Functionally identical to MIT, npm's default.

Copyleft licenses (require derivative works to be open source):
- GPL-3.0-or-later: Strong copyleft with patent protection.

For proprietary/private projects:
- UNLICENSED: Explicitly grants no rights.

View the complete SPDX License List at https://spdx.org/licenses/

Open your package.json and add the license field with a valid SPDX identifier:

{
  "name": "my-package",
  "version": "1.0.0",
  "license": "MIT"
}

For proprietary/unlicensed code:

{
  "license": "UNLICENSED",
  "private": true
}

Create a LICENSE file (no extension) in your project root directory.

1. Download the full license text from choosealicense.com or spdx.org/licenses/
2. Save as LICENSE in your project root
3. Update copyright year and author name if required

Example structure:

project/
├── LICENSE
├── package.json
├── src/
└── README.md

Validate that your license field uses proper SPDX format:

npm view . license

Common mistakes to avoid:
- "MIT License" instead of "MIT" (use short form only)
- "Apache 2.0" instead of "Apache-2.0" (missing hyphen)
- "GPLv3" instead of "GPL-3.0-or-later" (use proper SPDX)
- "UNLICENSE" instead of "UNLICENSED" (different meaning)