Gmail Labeler
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DR-003: GPL-3.0 License Choice

Date: 2025-01-15
Status: Active
Author: Sunchuangyu "Rin" Huang

Context

As a publicly released personal productivity tool, Gmail Labeler needs a license. The choice affects:

  • Derivative works - can others build commercial products on this codebase?
  • Contribution model - what terms do contributors agree to?
  • Philosophical alignment - what values does the license signal?

This is a personal project, not commercial software. The goal is to share a useful tool and demonstrate AI agent skill design, not to monetize or restrict use.

Decision

Use GPL-3.0 (GNU General Public License v3.0) - strong copyleft.

Key implications:

  • Users can: use, modify, distribute (including commercially)
  • Users must: keep the same GPL-3.0 license on derivative works, provide source code, state changes
  • Patent grant: explicit patent license from contributors
  • Anti-tivoization: modifications must remain user-installable (no locked-down hardware)

Options Considered

Option 1: MIT / Apache 2.0 (permissive)

  • Pro: Maximum freedom - anyone can do anything, including proprietary forks
  • Con: Someone could take the code, improve it, and close the improvements; community doesn't benefit from derivatives

Option 2: AGPL-3.0 (network copyleft)

  • Pro: Even stronger copyleft - SaaS deployments must share source
  • Con: Overkill for a personal productivity script; most users run locally, not as a service

Option 3: Creative Commons (e.g., CC BY-SA 4.0)

  • Pro: Familiar license, share-alike preserved
  • Con: CC licenses are for creative works, not software; no patent grant, no warranty disclaimer

Option 4: Custom license / all rights reserved

  • Pro: Maximum control
  • Con: No one will contribute; unclear legal terms; not OSI-approved

Option 5: Public domain / CC0

  • Pro: Absolute freedom, no restrictions
  • Con: No protections; can be incorporated into proprietary software with no attribution

Why

GPL-3.0 aligns with the project's values:

  1. Share-alike principle: If you improve this tool, others should benefit. The classification rules, the skill design, the provider taxonomy - these are useful beyond one person's inbox. GPL ensures derivatives stay open.

  2. Not a commercial product: This is a personal project shared publicly. I'm not selling it, so I have no reason to allow proprietary forks. If someone wants to commercialize it, GPL requires they also open-source their version.

  3. Contribution clarity: GPL is well-understood. Contributors know the terms upfront. No CLA (Contributor License Agreement) needed.

  4. Patent protection: Explicit patent grant protects users from contributor patent claims.

  5. Philosophical fit: Gmail Labeler is built on open-source AI models, open-source MCP servers, open-source libraries. Giving back to the commons via copyleft is consistent with that foundation.

Why not AGPL? The skill runs locally via Claude Code / Cursor, not as a hosted service. Network copyleft adds complexity without benefit.

What Happened

Since release (2 months):

  • 0 requests to relicense (as expected for a small personal project)
  • 0 GPL violations detected (also expected - not widely used yet)
  • 1 contribution (via PR) - contributor accepted GPL-3.0 terms implicitly by submitting

Community feedback:

  • No complaints
  • One user asked "can I use this at work?" - answer: yes, GPL allows commercial use; your employer must comply if they distribute a modified version (internal use only = no obligation)

What I'd change

  1. Add a FAQ section in README covering:

    • "Can I use this commercially?" (yes)
    • "Can I fork and modify?" (yes, must stay GPL)
    • "Do I need to share if I add personal rules?" (only if you distribute; private use has no obligation)

  2. Contributor guidelines - formalize a CONTRIBUTING.md stating:

    • By submitting a PR, you agree to GPL-3.0
    • Sign-off line in commits (DCO-style) for extra clarity

  3. License header in source files - currently only LICENSE file exists; should add SPDX header to .py scripts:

    # SPDX-License-Identifier: GPL-3.0-or-later

  4. Clarify web showcase license - the Next.js showcase (web/) is also GPL-3.0, but could be MIT separately if that encourages reuse. Current GPL applies to entire repo - consider dual-licensing just the web component.

  5. No CLA for now - but if the project grows, a Contributor License Agreement (allowing relicensing) might be useful for flexibility. For now, pure GPL is fine.

References

  • License file: LICENSE (root of repo)
  • GPL-3.0 text: https://www.gnu.org/licenses/gpl-3.0.en.html
  • Copyleft rationale: https://www.gnu.org/licenses/copyleft.en.html
  • Original skill: original/.agents/skills/gmail-labeler/ (also GPL-3.0)