Skill Creator Lite

A skill is a single markdown file with YAML frontmatter — that's the whole format. No build step, no deployment, no API. What makes it valuable isn't the format; it's whether the body encodes expertise Claude wouldn't apply by default. "Review code carefully" is worthless because the user could have typed it. "Flag O(n²) operations on collections over 100 items and propose the specific algorithmic fix" is a skill, because it makes a decision the user would otherwise have to make every time.

The skill teaches a scope check first. If your idea applies to everything in a project — code style, communication preferences, workflow rules — it belongs in CLAUDE.md, not a skill. If you'd use it once a month for a single input, a saved prompt is simpler. Skills are for recurring tasks complex enough that you'd spend two minutes writing the prompt each time. Code review, document generation, repeatable analysis frameworks — that's the sweet spot.

The five principles are the real content. Encode decisions, not just instructions (a skill that decides things for you beats a skill that reminds you to think). Use progressive disclosure — common case first, edge cases later, headers Claude can navigate. Explain the why so Claude can apply the principle to novel inputs. Be opinionated, because neutral skills produce neutral outputs. Specify the output format explicitly — tables, bullets, sections — because unstructured responses waste the reader's time.

Testing is treated as part of the build, not an afterthought. Run three to five real inputs through the skill. Check four dimensions: did Claude follow rules that contradict its defaults, does the output format match the spec, does it survive edge cases, and — most importantly — does the output differ from the no-skill baseline. If it doesn't differ, the skill isn't adding value. The 5-minute test at the end is the hardest one: hand the skill to someone with basic Claude experience, ask them to match its output by prompting manually in five minutes. If they can, your skill isn't encoding enough. If they can't, it's genuinely useful.