Cecil provides agent skills: instructions that AI coding agents (Claude Code, GitHub Copilot, Cursor, etc.) load to work with Cecil the right way, following its conventions.

Install

With the GitHub CLI:

gh skill install cecilapp/cecil

Or with npx skills:

npx skills add cecilapp/cecil

Usage

Once installed, ask your agent to create, build, configure or deploy a Cecil site, or to create a theme: it uses the matching skill automatically.

Examples of prompts:

• “Create a Cecil blog with an English and a French version.”
• “Add a projects section with a list of cards on the homepage.”
• “Turn the layouts of this site into a reusable Cecil theme.”

Language models read Markdown more easily than HTML. Cecil provides two output formats for them:

• llms: a llms.txt file, an index of the site;
• markdown: a Markdown version of each page.

Both are disabled by default.

llms.txt

Since version 8.114.0, the llms format renders the homepage as a llms.txt file at the root of the site. It contains:

• the site title and description;
• the links of the main menu (external URLs are ignored);
• the top-level sections and their pages (sub-sections are nested), with their title and description.

To enable it, add the format to the homepage:

output:
  pagetypeformats:
    homepage:
      llms: true

With the metatags template, the HTML homepage references the file with a <link rel="describedby" type="text/markdown"> tag.

Exclude content

To exclude a page or a section (and its pages) from llms.txt, set llms: false in its front matter:

---
title: "Legal notice"
llms: false
---

Unpublished and excluded sections are not listed.

Markdown pages

The markdown format renders a page as a Markdown file, next to its HTML version (e.g.: blog/post-1.md for blog/post-1/index.html). The file contains the title and the body of the page; a section lists its pages.

To render all pages and sections in Markdown:

output:
  pagetypeformats:
    page:
      markdown: true
    section:
      markdown: true

Or for a single page, with the output variable:

---
output: [html, markdown]
---

With the metatags template, the HTML page references its Markdown version with a <link rel="alternate" type="text/markdown"> tag. The links of llms.txt point to the Markdown version of the pages when it exists.

Templates

To customize these outputs, override the default templates in your layouts directory (see lookup rules):

• home.llms.twig: the llms.txt file;
• page.markdown.twig, list.markdown.twig and home.markdown.twig: the Markdown pages.

Cecil generates a robots.txt file that allows all crawlers. To block AI crawlers (or some of them), add your own rules by creating a page with the robots path:

pages/robots.md

---
layout: robots
output: txt
---
User-agent: GPTBot
Disallow: /

User-agent: ClaudeBot
Disallow: /

User-agent: Google-Extended
Disallow: /

The body of the page is appended to the default rules (see default pages).