Creating AI Coding Agent Skills

Recently Codex was updated to also leverage Agent Skills, established by Anthropic.

One friction point I have with this blog is creating the Astro frontmatter for the blog posts. I decided this would be a good skill for Codex.

To create the skill I added a new directory for the skill: .codex/skills/blog-template. Then added these instructions to a SKILL.md file in the directory’s root.

---
name: blog-template
description: Add or complete Astro Markdown frontmatter for blog posts (title, pubDate, description, tags) by inferring values from the post content. Use when asked to add headers/frontmatter to Markdown in src/content/blog, ensuring only these fields are present and only missing ones are filled.
---

# Blog Template

## Overview
- Add or complete an Astro frontmatter block for a blog post while leaving the body untouched.
- Only include `title`, `pubDate`, `description`, and `tags`; ignore other fields.
- If frontmatter already exists, preserve existing values and only fill missing fields.

## Workflow
1. Detect existing frontmatter at the top of the file. Keep provided values for the four allowed fields; drop any other keys from the new block.
2. Derive field values from the post content:
   - **title**: Prefer the first level-1 heading or the clearest inferred title; use sensible title case and avoid trailing punctuation.
   - **pubDate**: Keep existing value if present; otherwise set to today in `YYYY-MM-DD`.
   - **description**: Write a concise 1–2 sentence summary (often one line is enough). Multi-line is allowed using `|` but keep it brief and accurate.
   - **tags**: Infer key topics/subjects from the post. Rules: lowercase; hyphenate spaces; no punctuation; cap at 6; unique; required even if guessed. Prefer specific nouns over generic filler.
3. Emit a single frontmatter block at the very top in this form, then the untouched body:
   ```yaml
   ---
   title: |
     Example Title
   pubDate: 2025-12-01
   description: |
     One-sentence summary of the post.
   tags: ['topic-one', 'topic-two']
   ---

Tag selection hints

Choose the main themes, people, places, or technologies mentioned.
Skip redundant variants; prefer one canonical form (e.g., ai, not both ai and artificial-intelligence).
If content is thin, still provide tags that best match the subject matter.


So far I've been very happy with the results. I often lightly edit what it generates, but it gets me
close.

A future enhancement is to have Codex first generate a list of existing blog post tags, and then use
he list as a reference when generating tags for the new post.