This .NET Foundation guide, authored by .NET Foundation News and Blog, explains which licenses are compatible, clarifies common licensing myths, and outlines supported commercial strategies for project maintainers.

.NET Foundation License Compatibility Guide

Understanding What’s Compatible (and What’s Not)

What Licenses ARE Compatible

The .NET Foundation accepts projects that use permissive open source licenses. Permissive licenses automatically approved if they’re on the Open Source Initiative (OSI) approved list.

Examples of compatible permissive licenses include:

  • MIT License
  • Apache License 2.0
  • BSD licenses (2-clause, 3-clause)
  • ISC License

Key requirements:

  • The main codebase must use a permissive OSI-approved license
  • Mandatory dependencies should also be permissive (with exceptions for platform- or hardware-specific requirements)
  • Committers must agree to a Contributor License Agreement (CLA)
  • Copyright ownership must be defined and documented

What Licenses Are NOT Compatible

The .NET Foundation does not accept projects using copyleft licenses such as:

  • GPL (all versions)
  • AGPL
  • RPL
  • MPL (in some cases)
  • Other licenses with strong copyleft provisions

Reason: Copyleft licenses require all derivative works to be licensed similarly, which can deter corporate participation and doesn’t align with the Foundation’s priority for broad compatibility.

Business Models Supported by the Foundation

Permitted Strategies

  • Dual Licensing: Offer your project under a permissive license and a commercial license.
  • Commercial Services: Sell premium support, consulting, training, managed hosting, warranties, and SLAs.
  • GitHub Sponsors: Fund projects via GitHub’s sponsorship platform.
  • Company Formation: Spin up a company, provide paid support, enterprise offerings, and premium packages (core must stay permissive).

Principle: As long as the source is free, it’s compliant. Premium services and commercial models are allowed.

Clarifying the AutoMapper Departure

AutoMapper left the Foundation amicably after moving to the copyleft RPL license, which is no longer compatible with Foundation requirements. Monetization was not the issue—only the license change to a non-permissive one. Dual-licensing with a permissive license would have allowed continued membership.

Guidance for Project Maintainers

You can:

  • Use dual licensing
  • Start a company for your project
  • Charge for extra support/services
  • Offer paid/enterprise tiers
  • Use sponsorship platforms
  • Keep some features proprietary (core must be permissive)
  • Provide commercial warranties

You cannot:

  • Use copyleft (GPL, AGPL, RPL, etc.) for the core code
  • Require copyleft licenses in core dependencies

Foundation Policy

The .NET Foundation continues to review dual licensing frameworks but currently requires a permissive OSS license for project eligibility.

Questions?

For further clarification, contact the Foundation. Commercial sustainability is encouraged, so long as the core remains open and permissive.

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