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ADR-061 — Open-Core Dual Licensing

Status: Accepted Date: 2026-06-02

Context

The repository historically shipped a single root LICENSE (PolyForm Noncommercial 1.0.0) governing every file in the tree. That single grant covers both the freely reusable foundation (rtp-api, rtp-core) and the differentiating Pro-only features, and it forbids all commercial use.

Two goals motivated a change:

  1. Make the reusable foundation genuinely open for public use, including commercial use, so third-party addon authors and downstream projects can build on rtp-api / rtp-core without a noncommercial restriction.
  2. Keep the Pro-only features (the subsystems ADR-024 lists as "Drops" from the lite assembly: SQL/Redis persistence, the Folia adapter, the login reserve cache, the multilingual bootstrap, claim-plugin integrations, and the proxy / network-mode modules) under the existing noncommercial terms.

The two editions are built from one source tree (ADR-024): the RTP (lite) binary is a ShadowJar subset of the same rtp-core plus the Spigot/Paper (and Fabric) adapters; it does not contain any Pro-only source. This makes a clean open-core boundary possible without forking the codebase.

Decision

Dual-license the repository (open-core):

  • MIT (LICENSE-MIT at the repository root, mirrored as a module-local LICENSE in rtp-api/ and rtp-core/): the rtp-api and rtp-core modules, and the RTP (lite) binary distribution. These may be used, modified, and redistributed, including commercially, under the MIT License.
  • PolyForm Noncommercial 1.0.0 (the root LICENSE): all other source in the repository, i.e. the Pro-only features and the Pro plugin assembly.

The root LICENSE carries a preamble describing the split. Where a module or file ships a more specific LICENSE or SPDX header, that grant governs the file; otherwise the PolyForm Noncommercial terms apply.

Lite binary license

The lite assembly (ADR-024) bundles its in-jar LICENSE from LICENSE-MIT (renamed to LICENSE in the jar), not from the root PolyForm LICENSE. The liteJarStructureCheck Gradle audit asserts the lite jar's LICENSE entry contains the MIT text and does not contain the PolyForm Noncommercial text, so a regression that re-bundles the wrong license fails the build.

The Pro (shadowJar / remapJar) assembly continues to ship under the root PolyForm LICENSE.

Relationship to ADR-024

ADR-024 (RTP-lite Assembly Variant) is the structural prerequisite: because the lite jar already contains only the MIT-eligible subset (rtp-core + adapters, no Pro-only source), licensing the lite binary under MIT does not leak any Pro-only code. This ADR is additive to ADR-024 and does not change which classes/resources ship in either edition.

Alternatives Considered

Alternative Why Rejected
Keep a single PolyForm Noncommercial license for everything Blocks the stated goal of letting addon authors and downstream projects reuse rtp-api / rtp-core commercially.
License the two binaries differently but leave all source under one license Incoherent: MIT and PolyForm are one-directionally incompatible, so a shared file offered under both lets a consumer pick MIT and ignore PolyForm. A per-module/per-file boundary is required.
Split the Pro-only code into a separate private repository Largest effort; ADR-024 already isolates Pro-only code into distinct classes/source sets, so a per-module license boundary achieves the goal without a repo split.

Consequences

  • Positive.
  • rtp-api, rtp-core, and the lite binary are reusable under MIT, including commercially.
  • The lite jar ships the correct (MIT) license, enforced by a build-time audit.
  • The Pro-only differentiators remain noncommercial.
  • Negative / Trade-offs.
  • The licensing boundary must be maintained as code moves between modules: code that migrates into rtp-api / rtp-core becomes MIT, and Pro-only code must not be moved into those modules without intending to relicense it.
  • Re-licensing the shared core to MIT assumes the copyright holder controls those files; any third-party-copyright contribution to rtp-api / rtp-core would need contributor sign-off.

References

  • LICENSE — root PolyForm Noncommercial license with the dual-license preamble.
  • LICENSE-MIT — MIT license text bundled into the lite binary.
  • rtp-api/LICENSE, rtp-core/LICENSE — module-local MIT grants.
  • rtp-plugin/build.gradle — shadowLiteJar bundles LICENSE-MIT; liteJarStructureCheck asserts the lite jar ships the MIT license.
  • ADR-024 — RTP-lite Assembly Variant (the structural prerequisite).