MCP for Gantry 5 is a free add-on for MCP for J that lets your AI client read and change a Gantry 5 template: outlines and which pages use them, layouts, particles, styles and Gantry 5 Particle modules. Gantry spreads one site's design across a stack of outlines that inherit from each other, so the hardest question is usually where does this value actually come from? Every value these 21 tools report says which outline it lives in, and every change tells you which other outlines it also reaches.
Why this exists
Gantry 5 keeps its settings in YAML files, one set per outline, with inheritance on top. Changing the copyright line or a colour is easy once you know which outline and which file to open, and finding that out is the slow part. This add-on reads those files the way Gantry does and answers in plain language, so "change the footer copyright to 2027" lands in the right place the first time.
What Claude can do
There are 21 tools, grouped the way you'd reach for them.
| Area | Tools | What you can do |
|---|---|---|
| Themes and outlines | 6 | List themes and outlines, read an outline with its full inheritance chain, see which pages use which outline, change those assignments, and duplicate an outline as a copy or as one that inherits from its source. |
| Layouts | 2 | Read an outline's layout, and list the module positions and module instances it renders, with the Joomla modules each one shows and any positions the layout never renders. |
| Particles | 5 | List particle types, read and change a particle in an outline, and read and change particle defaults. |
| Styles | 2 | Read and change an outline's styles, such as colours and fonts. |
| Particle modules | 2 | List and change Gantry 5 Particle modules. |
| Backups | 2 | List the backups these tools take before every change, and restore one. |
| Diagnostics | 2 | A health check and Gantry's own Clear Cache. |
Installing it
You'll need Joomla 5 or 6, PHP 8.2 or later, MCP for J, and Gantry 5 itself, which is free. On Joomla 6 you need Gantry 5.6.2 or later; 5.6.0 and 5.6.1 only run on Joomla 5. The add-on was built against Gantry 5.6.4 with the Helium 5.6.4 theme.
- Open Components โ MCP for J โ Browse MCP Add-Ons and click Install on this add-on. You can also download the ZIP above and install it through System โ Install โ Extensions.
- That's the whole install. The plugin switches itself on, and the tools show up in your AI client the next time it lists them.
If MCP for J isn't installed, the plugin installs switched off and tells you why, rather than leaving you with tools that go nowhere.
Using it
Start with "Check my Gantry 5 setup". The health check looks at your Gantry and Joomla versions together, outlines whose inheritance points at something that's gone, YAML files Gantry can't read, and outline folders left behind by deleted template styles. Then ask for what you want: "Which outline does the About page use?", "Make the accent colour darker on the Blog outline" or "Copy the Home outline so I can try a new layout".
When a setting is inherited, the tools won't quietly copy it into the outline you named. They tell you which outline it comes from, so you can decide whether to change it there (and everywhere that inherits it) or break the link.
A few things about Gantry are worth knowing:
- Gantry's own admin can overwrite an outline. For a template style without a
configurationsetting, Gantry's outline list copies the preset over the outline's own files, and Gantry's installer creates every style that way. The write tools add that setting first, and the health check warns about any style still missing it. - Deleting a template style that other outlines inherit from makes them fall back to a preset, and Gantry recreates a folder for the deleted outline on the next page view. The health check reports both.
- Gantry's configuration files can be read over the web, so keep passwords and keys out of particle settings.
Permissions and security
The tools check the same Joomla permissions as the screens they stand in for: managing and editing templates for outlines, particles and styles, editing menus for outline assignments, and managing and editing modules for Gantry 5 Particle modules. It's checked for the person whose MCP connection makes the request, so your AI client can't do anything that person couldn't do in the admin.
Reading never changes anything. Gantry's own layout reader saves files when its index is out of date, so these tools read Gantry's YAML themselves instead. A change writes one file, key by key, only under the theme's custom/config folder, after taking a backup that restore_gantry5_backup can put back. Keys and values are checked against Gantry's own blueprints, and the new file is read back before it replaces the old one. A Custom HTML particle with "Process Twig" switched on runs its content as server-side code, so only a Super User can switch that on or change such content.
Why it's free
Gantry 5 is free, so this add-on is free too.
This is version 1.0.0. All 21 tools were driven end to end on Joomla 6.2.0 with PHP 8.3 against Gantry 5.6.4 and Helium, and every change was checked in the files, the database and on a rendered page, then restored from its backup. Themes with a parent theme, older layout formats and Joomla 5 haven't been tried yet. If your site uses them, start with the health check, and I'd like to hear how it goes.
Open source
GPL-2.0-or-later, the same license as Joomla itself. Source lives on GitHub.
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