wp-plugin-directory-guidelines

What this skill does

## Overview

Authoritative reference for the 18 WordPress.org Plugin Directory guidelines. Covers GPL licensing, plugin naming/trademark rules, trialware restrictions, and all other submission requirements.

## When to use

Use this skill when you need to:
- Review a WordPress plugin for compliance with the WordPress.org Plugin Directory guidelines
- Check GPL license compatibility for a plugin or its bundled libraries
- Verify license headers in plugin files
- Identify common guideline violations before submission
- Answer questions about what is or is not allowed on WordPress.org
- Evaluate premium/upsell flows, license checks, or freemium positioning
- Review "teaser" or "preview" UI for trialware violations

## Inputs required

- Plugin source code (or specific files to review)
- Optional: plugin readme and plugin header metadata for naming and license checks

## Procedure

1. Check the plugin's license header against the **Valid License Headers** section below.
2. Walk through the **18 Guidelines** checklist, paying special attention to Guidelines 1, 4, 5, 7, 8, and 17.
3. Confirm trialware/freemium compliance using the checklist in [guideline-review-checklist.md](references/guideline-review-checklist.md) (Guideline 5 section).
4. For bundled third-party code, verify license compatibility against **GPL-Compatible Licenses (Quick)** below.
5. Flag matches from **Common GPL Violations (Quick)** below.
6. For edge cases, consult the detailed references and the [GNU GPL FAQ](https://www.gnu.org/licenses/gpl-faq.html).

## 18-Guideline Review Checklist

Use the detailed, per-guideline checklist in [guideline-review-checklist.md](references/guideline-review-checklist.md). Load this reference file only when a full guideline audit is requested.

## GPL Compliance (Guideline 1 in Detail)

Use [gpl-compliance.md](references/gpl-compliance.md) for full license tables, compatibility nuances, and examples. Keep this inline section as a quick decision aid.

### Verification (Licensing)

- Every licensing-related issue must cite **Guideline 1** and include the file path and exact license string.
- Confirm compatibility claims against **GPL-Compatible Licenses (Quick)** and escalate ambiguous licenses.

### Failure modes (Licensing)

- If a license is not clearly GPL-compatible, do not guess. Check the [GNU license list](https://www.gnu.org/licenses/license-list.html).
- For dual-license packages, verify both licenses and redistribution terms.

### Quick Reference: WordPress GPL Requirements

- WordPress is **GPLv2 or later**.
- Plugins distributed on WordPress.org must be 100% GPL-compatible (code and assets).
- Include a valid `License:` header and `License URI:` in the main plugin file.
- Do not add restrictions that conflict with GPL freedoms.

### Valid License Headers

## GPL Versions Summary

| Version | Year | Key Addition |
|---------|------|--------------|
| GPLv1 | 1989 | Base copyleft: share-alike for modifications |
| GPLv2 | 1991 | "Liberty or death" clause (Section 7), clearer distribution terms |
| GPLv3 | 2007 | Anti-tivoization, explicit patent grants, compatibility provisions |

WordPress uses **GPLv2 or later**, meaning plugins can use GPLv2, GPLv3, or "GPLv2 or later".

For full license texts, see:
- [GNU General Public License v1](https://www.gnu.org/licenses/gpl-1.0.html)
- [GNU General Public License v2](https://www.gnu.org/licenses/gpl-2.0.html)
- [GNU General Public License v3](https://www.gnu.org/licenses/gpl-3.0.html)

## License Compliance Checklist

When reviewing a plugin, verify:

- [ ] Main plugin file has a valid `License:` header (e.g., `GPL-2.0-or-later`, `GPL-2.0+`, `GPLv2 or later`)
- [ ] Main plugin file has a `License URI:` header pointing to the GPL text
- [ ] If bundled libraries exist, each has a GPL-compatible license
- [ ] No "split licensing" (e.g., code GPL but premium features proprietary)
- [ ] No additional restrictions beyond what GPL allows
- [ ] No clauses restricting commercial use, modification, or redistribution
- [ ] No obfuscated code (violates the spirit of source code availability)

## Valid License Headers for WordPress Plugins

```
License: GPL-2.0-or-later
License URI: https://www.gnu.org/licenses/gpl-2.0.html
```

```text
License: GPL-3.0-or-later
License URI: https://www.gnu.org/licenses/gpl-3.0.html
```

```text
License: GPLv2 or later
License URI: https://www.gnu.org/licenses/gpl-2.0.html
```

### GPL-Compatible Licenses (Quick)

- Safe defaults: GPL-2.0-or-later, GPL-3.0-or-later.
- Commonly accepted permissive families: MIT/Expat, BSD, ISC, zlib, Boost.
- Conditional compatibility requires care: Apache-2.0 and MPL-2.0 (verify usage context).
- For full accepted and rejected identifiers, use [gpl-compliance.md](references/gpl-compliance.md).

### Common GPL Violations (Quick)

- Split licensing that restricts distributed code.
- Obfuscated or non-corresponding source distribution.
- Restrictive clauses (non-commercial, no-resale, forced backlink).
- Bundling GPL-incompatible libraries or assets.

## Plugin Naming Rules (Guideline 17)

Use [naming-rules.md](references/naming-rules.md) for full trademark lists, slug blocks, and naming examples. Keep this inline checklist for quick screening.

### Naming Checklist (Quick)

- Name is not a placeholder and has at least 5 alphanumeric characters.
- Header name and readme name match.
- Name is specific and function-related; avoid keyword stuffing.
- Trademark/project names appear only after connectors like `for`, `with`, `using`, `and`.
- No banned/discouraged terms or trademark portmanteaus.
- Slug is lowercase, hyphenated, <= 50 chars, and avoids blocked terms.