Software License Comparison Guide

The main spectrum goes from most permissive to most restrictive:
Public Domain (CC0, Unlicense) - Zero restrictions
Permissive (MIT, Apache, BSD) - Use anywhere, just keep attribution
Weak Copyleft (MPL, LGPL) - Share back changes to the licensed code only
Strong Copyleft (GPL, AGPL) - Everything that uses this code must also be open source

For most projects, you'll want either:
MIT - If you want maximum adoption and simplicity
Apache 2.0 - If you want maximum adoption with better legal protections
GPL-3.0 - If you want to ensure derivative works stay open source
AGPL-3.0 - If you want to prevent companies from making proprietary cloud services with your code

🟢 Permissive Licenses (Most Freedom)

MIT License

What it means: Do whatever you want, just keep the copyright notice.

  • ✅ Use commercially
  • ✅ Modify freely
  • ✅ Distribute freely
  • ✅ Use in proprietary software
  • ❌ No warranty/liability protection for author

When to use: You want maximum adoption and don't care if others profit from your work without giving back.

Apache License 2.0

What it means: Like MIT, but with extra legal protections.

  • ✅ Everything MIT allows
  • ✅ Patent protection (contributors can't sue you over patents)
  • ✅ Trademark protection
  • ✅ Better legal language

When to use: You want maximum adoption but with better legal safety. Popular for enterprise software.

BSD 2-Clause "Simplified"

What it means: Almost identical to MIT.

  • ✅ Same freedoms as MIT
  • ✅ Slightly different wording

When to use: When you want MIT-like freedom but prefer BSD's wording.

BSD 3-Clause "New" or "Revised"

What it means: Like BSD 2-Clause + you can't use the author's name to endorse derivatives.

  • ✅ Same as BSD 2-Clause
  • ❌ Can't use original author's name for marketing

When to use: When you want BSD freedom but don't want others using your name/reputation.

Boost Software License 1.0

What it means: Even more permissive than MIT - no attribution required in binaries.

  • ✅ Use anywhere without attribution in compiled code
  • ✅ Only need attribution in source distributions

When to use: For libraries where you want zero friction for users.

🔵 Public Domain (Maximum Freedom)

Creative Commons Zero v1.0 Universal (CC0)

What it means: "I give up all rights to this code."

  • ✅ Literally no restrictions
  • ✅ No attribution required

When to use: You want to donate your code to humanity with zero strings attached.

The Unlicense

What it means: Same as CC0 - puts code in public domain.

  • ✅ No restrictions whatsoever

When to use: Same as CC0, alternative wording for public domain dedication.

🟡 Weak Copyleft (Some Restrictions)

Mozilla Public License 2.0 (MPL-2.0)

What it means: File-level copyleft - modifications to MPL files must stay MPL.

  • ✅ Can combine with proprietary code
  • ✅ Can use in commercial products
  • ❌ Changes to MPL-licensed files must be shared back
  • ✅ Can add your own proprietary files

When to use: You want improvements to your specific code shared back, but allow commercial use.

Eclipse Public License 2.0

What it means: Similar to MPL but for modules/components.

  • ✅ Can combine with proprietary code
  • ❌ Changes to EPL components must be shared back

When to use: Similar to MPL, popular in Java enterprise world.

GNU Lesser General Public License v2.1 (LGPL)

What it means: Library-focused copyleft - dynamic linking is usually okay.

  • ✅ Can link to LGPL libraries from proprietary software
  • ❌ If you modify the LGPL library itself, must share changes
  • ⚠️ Static linking can be problematic

When to use: For libraries where you want improvements shared back but allow proprietary applications.

🔴 Strong Copyleft (Most Restrictions)

GNU General Public License v2.0 (GPL-2.0)

What it means: "If you use this, your entire program must be GPL too."

  • ❌ Cannot combine with proprietary code
  • ❌ Entire application must be GPL if it uses GPL code
  • ✅ Ensures all derivative works remain free

When to use: You want to ensure your code and anything that uses it stays free/open source forever.

GNU Affero General Public License v3.0 (AGPL)

What it means: Like GPL but covers network/web services too.

  • ❌ Everything GPL restricts
  • ❌ If users access your AGPL software over a network, you must provide source
  • ❌ Closes the "SaaS loophole"

When to use: You want to prevent companies from using your code in proprietary web services without sharing back.

📊 Quick Decision Matrix

Your Goal Recommended License
Maximum adoption, don't care about giving back MIT or Apache 2.0
Want legal protections, enterprise-friendly Apache 2.0
Want improvements to your code shared back MPL-2.0 or LGPL-2.1
Want everything to stay open source forever GPL-2.0
Prevent proprietary SaaS/cloud services AGPL-3.0
Give code to humanity with zero restrictions CC0 or Unlicense

🚨 Key Warnings

  • GPL is viral - it "infects" any code that uses it
  • AGPL is even more viral - covers network services too
  • Patent issues - Apache 2.0 provides better patent protection than MIT
  • Mixing licenses - Be very careful about license compatibility
  • Legal advice - When in doubt, consult a lawyer

💡 Most Common Choices

  1. MIT - Simple, widely understood, maximum adoption
  2. Apache 2.0 - Enterprise-friendly with patent protection
  3. GPL-3.0 - When you want everything to stay open source
  4. AGPL-3.0 - When you want to prevent proprietary cloud services