Choosing a License¶

Selecting a license is one of the most important decisions you'll make for your project. This guide helps you think through the considerations and arrive at the right choice.

The Decision Framework¶

Start with these questions:

1. Is this software or creative work?¶

Work Type	Consider
Software (code)	MIT, Apache 2.0, GPL, MPL
Data or databases	CC0, CC BY, ODbL
Documentation	CC BY, CC BY-SA
Images, video, music	CC licenses
Mixed	Multiple licenses for different components

Don't use Creative Commons for code

CC licenses don't address software-specific concerns like source code, compilation, and linking. Use software licenses for software.

2. What do you want to allow?¶

Be honest about what matters to you:

Priority	Suggests
Maximum adoption	Permissive (MIT, Apache 2.0, CC BY)
Keep improvements open	Copyleft (GPL, CC BY-SA)
Prevent commercial exploitation	NC licenses (not open source)
No restrictions at all	CC0, Unlicense

3. What community are you joining?¶

Ecosystem norms matter:

Ecosystem	Common Licenses
JavaScript/Node	MIT
Java/Enterprise	Apache 2.0
Linux/GNU	GPL
Data science	MIT, Apache 2.0, CC0 for data
Academic	CC BY for papers, varied for code
Rust	MIT + Apache 2.0 (dual)
Go	BSD-3-Clause

Matching your ecosystem reduces friction.

The Flowchart¶

                    START
                      │
                      ▼
            ┌─────────────────┐
            │ Do you want     │
            │ attribution?    │
            └────────┬────────┘
                     │
           ┌─────────┴─────────┐
           │                   │
          No                  Yes
           │                   │
           ▼                   ▼
     ┌──────────┐    ┌─────────────────┐
     │ CC0 or   │    │ Should changes  │
     │ Unlicense│    │ stay open?      │
     └──────────┘    └────────┬────────┘
                              │
                    ┌─────────┴─────────┐
                    │                   │
                   No                  Yes
                    │                   │
                    ▼                   ▼
         ┌──────────────────┐   ┌──────────────────┐
         │ Is patent        │   │ How viral        │
         │ protection       │   │ should it be?    │
         │ important?       │   └────────┬─────────┘
         └────────┬─────────┘            │
                  │              ┌───────┼───────┐
           ┌──────┴──────┐       │       │       │
           │             │       ▼       ▼       ▼
          No            Yes    Whole   Files   Library
           │             │     work    only    only
           ▼             ▼       │       │       │
        ┌─────┐    ┌──────────┐  ▼       ▼       ▼
        │ MIT │    │Apache 2.0│ GPL     MPL    LGPL
        └─────┘    └──────────┘

Common Scenarios¶

"I want people to use this without hassle"

Choose: MIT — Simple, understood everywhere, imposes minimal burden. The default choice for maximum adoption.
"I want credit but don't care about contributions back"

Choose: MIT or Apache 2.0 — Both require attribution. Apache 2.0 adds patent protection for larger projects or enterprise use.
"I want improvements to come back to the community"

Choose: GPL v3 or AGPL — Strong copyleft ensures public improvements must be shared. AGPL extends this to SaaS.
"I'm building a library for wide use"

Choose: MIT, Apache 2.0, or LGPL — MIT/Apache for simplicity; LGPL if you want library improvements shared but allow proprietary use.
"This is a web service that might be hosted by others"

Choose: AGPL — Closes the SaaS loophole. Competitors must share improvements when they host your code.
"I'm publishing research data"

Choose: CC0 — Maximum reuse for data. Academic citation norms provide attribution even without legal requirement.
"I'm writing documentation"

Choose: CC BY or CC BY-SA — CC BY for free use with credit; CC BY-SA to keep adaptations open.
"I want to dual-license for business"

Choose: GPL + commercial, or AGPL + commercial — Open source under copyleft for community, sell commercial licenses for proprietary use.

License Compatibility Considerations¶

If your project incorporates existing code, you must comply with its license:

Your New Code	Can Include	Cannot Include
MIT	MIT, BSD, CC0	GPL (without becoming GPL)
Apache 2.0	MIT, BSD, CC0	GPL v2
GPL v3	MIT, BSD, Apache 2.0, LGPL, GPL v2	Differently-copylefted code
Proprietary	MIT, BSD, Apache 2.0, LGPL (carefully)	GPL, AGPL

When in doubt, check the specific licenses involved.

How to Apply a License¶

For software:¶

Add a LICENSE or LICENSE.txt file with the full license text
Add a copyright notice to the top of source files (optional but common)
If using Apache 2.0, consider adding a NOTICE file

For creative works:¶

Include license information with the work
Use CC license badges where visible
Include license in metadata (EXIF for images, etc.)

Template for source files:¶

// SPDX-License-Identifier: MIT
// Copyright (c) 2026 Your Name

SPDX identifiers are machine-readable and increasingly standard.

What If I Change My Mind?¶

You can always add permissions¶

You can release future versions under a more permissive license. This doesn't affect existing releases.

You can't revoke past permissions¶

Once you've licensed something, recipients have those rights. You can't take them back.

If others have contributed, relicensing typically requires agreement from all contributors. This is why Contributor License Agreements (CLAs) exist.

Final Advice¶

When in doubt:

For software: Start with MIT unless you have specific reasons for something else
For data: Use CC0
For documentation: Use CC BY
Always include a LICENSE file—ambiguity helps no one