Add JSON as an alternative to PHP/CSS file headers for plugin and theme metadata

[retlehs]

Trac ticket: https://core.trac.wordpress.org/ticket/24152

This adds support for declaring plugin and theme metadata in JSON files as an alternative to PHP/CSS comment-based file headers.

• Plugins can now use a plugin.json file alongside the main PHP file
• Themes can now declare metadata in the metadata property of theme.json
• JSON metadata takes priority when present; existing file headers work as a fallback
• Backwards compatible fallback behavior remains: if JSON metadata is missing or invalid, existing file headers are still used

Motivation

PHP/CSS file headers are parsed via regex on the first 8KB of a file. JSON provides a structured, machine-readable, language-agnostic alternative that:

• Eliminates regex parsing fragility
• Aligns with modern conventions
• Allows themes to work without style.css (block themes already don't need one for styling)

See: WordPress File Headers Have Overstayed Their Welcome

Examples

plugin.json

{
  "name": "My Plugin",
  "uri": "https://example.com/my-plugin",
  "description": "A short description of the plugin.",
  "author": "Plugin Author",
  "authorUri": "https://example.com",
  "version": "1.0.0",
  "textDomain": "my-plugin",
  "requires": {
    "wordpress": "7.0",
    "php": "8.0",
    "plugins": ["woocommerce", "jetpack"]
  },
  "network": true,
  "mainFile": "bootstrap.php"
}

theme.json (metadata property)

{
  "version": 3,
  "metadata": {
    "name": "My Theme",
    "uri": "https://example.com/my-theme",
    "description": "A short description of the theme.",
    "author": "Theme Author",
    "authorUri": "https://example.com",
    "version": "1.0.0",
    "tags": ["blog", "one-column"],
    "textDomain": "my-theme",
    "template": "parent-theme"
  },
  "settings": { ... },
  "styles": { ... }
}

Other examples from my demo repo: https://github.com/retlehs/json-metadata-theme-and-plugin

Changes

Plugin metadata (plugin.json)

• New _get_plugin_json_data() function reads plugin.json from a plugin's directory
• get_plugin_data() checks for JSON metadata first, then falls back to PHP file headers
• Only applies to direct children of WP_PLUGIN_DIR (not mu-plugins or drop-ins)
• Supports a mainFile property to designate the main entry point (defaults to {dir-name}/{dir-name}.php)
• requires.plugins array maps to comma-separated RequiresPlugins header format
• network field uses strict boolean checking (true only)
• Uses silent JSON decoding (not wp_json_file_decode()) to avoid errors during enumeration
• Files outside direct child plugin directories (including mu-plugin subdirectories and drop-ins) are ignored
• JSON parsing honors headers registered via the existing extra_plugin_headers filter

Theme metadata (theme.json → metadata)

• New read_json_metadata() private method on WP_Theme reads metadata from theme.json
• Constructor tries JSON metadata before style.css headers
• Themes with theme.json metadata can now work without a style.css file
• Updated validate_current_theme() to allow active themes (including child themes) without style.css when theme.json contains valid metadata.name
• Uses silent JSON decoding to avoid errors when enumerating themes with malformed theme.json
• JSON metadata parsing honors headers registered via the existing extra_theme_headers filter

Schema notes

The theme.json schema (maintained in the Gutenberg repo) will need a companion PR to add the metadata property definition.

Schema publication/documentation for plugin.json will need to be done.

Testing

npm run test:php -- --filter "Tests_Admin_IncludesPluginJsonMetadata|Tests_Admin_WPPluginDependencies_Initialize|Tests_Theme_ThemeDir|Tests_Theme_wpThemeJsonMetadata"

All filtered tests passed locally in Docker

Demo

See https://github.com/retlehs/json-metadata-theme-and-plugin for an example plugin and theme, along with instructions on how to setup your local environment with this PR

Plugin Metadata	Theme Metadata	Theme Front End

Use of AI Tools

This PR was authored with Claude Code and Codex. Both were used for implementation, test writing, and code review. I reviewed and validated all changes, and ran tests locally in Docker.

[github-actions]

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[github-actions]

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[github-actions]

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[QWp6t]

LGTM!

[sybrew]

This odd behavior that prevents custom keys stems from https://core.trac.wordpress.org/ticket/8964 — no valid reason was given.

Can we rectify it? It would allow us to quickly deprecate and assign alternative names without changing keys.