Use when reviewing WordPress plugins for GPL compliance, checking license headers or compatibility, evaluating upsell/freemium/trialware patterns, validating plugin naming or trademark rules, checking plugin slugs, understanding why a plugin was rejected from WordPress.org, or answering any question

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 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.

wp-plugin-directory-guidelines