Building Reusable Skills with SKILL.md

Learning objectives

• State the two required SKILL.md frontmatter fields and explain progressive disclosure.
• Write a trigger-worthy skill description using concrete phrases, not vague language.
• Build one working Reddit skill end to end and verify it triggers correctly.
• Explain why Skills work identically across Claude.ai, Claude Code, and the API.
• Identify an existing Anthropic or third-party skill worth forking rather than building from scratch.

Prerequisites: Module 6.1 in full.

Core concepts

A Skill is a folder containing a SKILL.md file whose YAML frontmatter requires only two fields, name and description, and Claude auto-loads the skill when a task's description matches. Skills work identically across Claude.ai, Claude Code, and the API: author once, run everywhere (Anthropic Agent Skills docs, platform.claude.com). The mechanism that makes this scale without bloating every conversation is "progressive disclosure": only the name and description, a few dozen tokens, stay resident in context until a skill actually triggers, at which point the full SKILL.md plus any bundled scripts or templates load on demand (Anthropic Engineering, "Equipping agents for the real world with Agent Skills").

The description field is not documentation, it is the trigger, and vague descriptions cause misfires. Anthropic's own best-practices guidance stresses listing concrete trigger phrases: a brand-voice skill should trigger on "brand guidelines," "voice and tone," "writing style guide," not on a generic "helps with writing" (platform.claude.com skill best-practices). For Reddit work, that means naming the exact tasks a skill should catch.

---
name: reddit-intent-scorer
description: >
  Scores a Reddit thread's buying intent on a 0-100 scale using our team's
  labeled examples. Trigger on "score this thread", "is this buying intent",
  "check this Reddit post", or when pasted Reddit thread text is followed by
  a request to evaluate it. Also flags thread age against the first-hour rule
  and comment count against the under-10-comment rule from our Stage 4 spec.
---

## Instructions
1. Compare the pasted thread against the labeled examples in
   reddit-context/scored-examples.md.
2. Output: score (0-100), one-line reasoning, thread age in hours, comment
   count, and a PRIORITY/LOW-PRIORITY flag per our first-hour and
   under-10-comment rules.
3. Never draft a reply in this skill, scoring only. Hand off to
   reddit-reply-drafter for drafting.

Build your first real skill on exactly this pattern: a reddit-intent-scorer folder with the SKILL.md above and a bundled scored-examples.md file holding your labeled Stage 4 examples. Test it by pasting a new thread into a plain Claude.ai chat inside your Reddit Marketing Ops Project and confirming the skill triggers without you having to name it explicitly, if it doesn't trigger reliably, the fix is almost always the description, not the instructions body. For a faster start, Anthropic's own public repository of example Skills gives working SKILL.md templates to fork rather than write from scratch, and its companion PDF guide covers directory organization and progressive disclosure end to end.

Video lessons

Supporting reading

• Agent Skills - Overview, Claude Platform Docs (https://platform.claude.com/docs/en/agents-and-tools/agent-skills/overview), the authoritative primary source on SKILL.md structure and cross-surface portability.
• Skill authoring best practices, Claude Platform Docs (https://platform.claude.com/docs/en/agents-and-tools/agent-skills/best-practices), the how-to for writing trigger descriptions that actually fire reliably.
• anthropics/skills (GitHub) (https://github.com/anthropics/skills), official example Skills and SKILL.md templates to study and fork.
• The Complete Guide to Building Skills for Claude (PDF), Anthropic (https://resources.anthropic.com/hubfs/The-Complete-Guide-to-Building-Skill-for-Claude.pdf), a single end-to-end reference covering everything in this lesson.

Exercise

Build the reddit-intent-scorer skill above with at least five real labeled examples. Test it in three separate conversations, confirming it triggers without explicit naming each time.

Assignment

Submit the finished skill folder (SKILL.md plus example file) and a short log of your first three trigger tests, noting any description rewrite you needed to make it fire reliably.

Claude workflow

• Prompt: "Here's a new Reddit thread: {{paste_thread_text}}. Score this." (No skill name mentioned, the point is testing that the description alone triggers reddit-intent-scorer.)
• Skill idea: the reddit-intent-scorer itself, extended over time with more labeled examples as your team's judgment calibrates.
• Automation: none yet, this lesson is about authoring one reliable skill by hand before Module 6.3 wires skills into a scheduled pipeline.

Expected outcomes

• Working reddit-intent-scorer skill, triggering reliably across at least three test conversations.
• Can state the two required frontmatter fields and explain progressive disclosure without notes.
• Can identify one existing Anthropic example skill worth forking for a second Reddit-ops task.