skill-diff

Single-script skill that compares a customized skill against the original. It reads the local skill's based_on: frontmatter, fetches the upstream SKILL.md fresh from GitHub (never from a local marketplace copy, which may be stale), and prints a raw textual diff preceded by a short summary header. Claude then interprets that output into a markdown comparison table plus a dual summary: local customizations and upstream changes worth adopting.

What it shows (and what it does not)

The diff is a two-way comparison between your local SKILL.md and the current upstream HEAD — i.e. current divergence. For skills that track upstream closely this is effectively "what changed upstream." For skills that are substantial rewrites (e.g. plan, work), the diff is a full comparison, not a "since-fork delta"; the header flags this so the output is not misread. A true three-way "what changed upstream since I forked" view is a future addition (see "Fork-point ref", below).

The tool only reports drift. It never edits a skill, never applies upstream changes, and never rewrites based_on. It compares SKILL.md only — bundled scripts/ and references/ are not diffed (though substantially different file counts are reported in the header). The upstream skill is fetched fresh on each run, so the diff always reflects the latest upstream state, not a cached or local copy.

Requirements

• gh installed and authenticated (gh auth status). The script fetches upstream content through gh api, so private upstreams resolve transparently under your GitHub auth.

Usage

bash skills/skill-diff/scripts/compare.sh <skill-name>