Open Source License Guide

What each license actually means — in plain English. 11 licenses documented.

MIT License

Do whatever you want. Just keep the copyright notice.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

Apache License 2.0

Like MIT, but with an explicit patent grant and contribution terms.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

GNU General Public License v3.0

Use freely, but if you distribute modifications, you must release your source code under GPL too.

copyleft
Commercial: Modify: Must open source: YesPatent grant: Attribution: Required

GNU Affero General Public License v3.0

Like GPL, but the copyleft extends to network use. If you run it as a service, you must share your source.

strong copyleft
Commercial: Modify: Must open source: YesPatent grant: Attribution: Required

BSD 2-Clause License

Almost identical to MIT. Keep the copyright notice, that's it.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

GNU Lesser General Public License v3.0

Copyleft for the library itself, but you can link to it from proprietary code.

weak copyleft
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

Business Source License 1.1

Source code is visible but you cannot use it commercially as a competing service. Converts to open source after a set date.

source available
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

Mozilla Public License 2.0

File-level copyleft. Modified files must be shared, but your other files can be proprietary.

weak copyleft
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

BSD 3-Clause "New" License

Do whatever you want. Keep the copyright. Don't use the author's name to endorse your product.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

ISC License

Functionally identical to MIT but shorter. Do whatever you want, keep the copyright.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Required

The Unlicense

Public domain dedication. No restrictions whatsoever — not even attribution required.

permissive
Commercial: Modify: Must open source: NoPatent grant: Attribution: Not required

Quick Reference

Permissive — do anything, keep the copyright
Weak Copyleft — share modified files only
Copyleft — share all modifications
Strong Copyleft — share even for SaaS/network use