Default branch: !git symbolic-ref refs/remotes/origin/HEAD --short 2>/dev/null | sed 's|.*/||' || echo main

Report only what changed. Locate; don't fix. If no URL in $ARGUMENTS, ask for one.

Parse $ARGUMENTS: strip --branch <name> if present → branch mode. If --branch has no value, use the default branch above. Remainder is the URL.

When to Use

• Use this skill when the task matches this description: Diff a live page's accessibility violations against a baseline — by default compares uncommitted changes (stash-based), or pass --branch [] to diff against a branch. Reports only new violations introduced, violations fixed, and pre-existing count. Use scan for a full audit with no diffing.

1. Audit

PORT=$(npx -y @accesslint/chrome@latest ensure | node -e 'process.stdin.on("data",d=>process.stdout.write(""+JSON.parse(d).port))')

Stash mode (default — uncommitted changes). Tell the user first: "Running in diff mode — stashing your changes to capture a baseline, then restoring. Your working tree will be fully restored." If git stash push fails, warn and exit.

git stash push -u -m "accesslint-diff-baseline"
npx -y @accesslint/cli@latest "<url>" --port "$PORT" --snapshot accesslint-diff --snapshot-dir /tmp --update-snapshot
git stash pop && sleep 2
npx -y @accesslint/cli@latest "<url>" --port "$PORT" --snapshot accesslint-diff --snapshot-dir /tmp --format json

Branch mode (--branch <name>). Tell the user first: "Diffing against <name> — checking out that branch to capture a baseline, then restoring. Your working tree will be fully restored."

Branch switching triggers a rebuild but not a browser reload — the CLI opens a fresh tab each time so it always reads the current build. Use --wait-for "<selector>" to gate the audit until the rebuild is ready; without it, warn the user that a slow build may yield a stale baseline.

Keep the branch value in the quoted branch variable below; never paste or evaluate a branch name as shell syntax.

git diff --quiet && git diff --cached --quiet || git stash push -u -m "accesslint-diff-branch"
branch="<branch>"
git check-ref-format --branch "$branch" >/dev/null
case "$branch" in -*) echo "Refusing option-like branch name: $branch" >&2; exit 1 ;; esac
git rev-parse --verify --quiet "$branch^{commit}" >/dev/null
git switch "$branch"
npx -y @accesslint/cli@latest "<url>" --port "$PORT" --snapshot accesslint-diff --snapshot-dir /tmp --update-snapshot [--wait-for "<selector>"]
git switch - && git stash pop 2>/dev/null
npx -y @accesslint/cli@latest "<url>" --port "$PORT" --snapshot accesslint-diff --snapshot-dir /tmp --format json [--wait-for "<selector>"]

Pass --selector, --include-aaa to both runs.

2. Report

Accessibility diff — http://localhost:3000/ vs main (94 rules, live DOM)
2 new · 1 fixed · 4 pre-existing hidden

New — Critical
- color-contrast — 2.1:1 (needs 4.5:1), #bbb on #fff
    where: main > p.subtitle   fix: darken to #767676
Fixed
- img-alt — <img src="old.jpg"> (no longer present)

Each new violation: where (selector verbatim + file:line (symbol) if source present — never fabricate), evidence, fix (mechanical change or NEEDS HUMAN).

Don't edit. For fixes: apply mechanical ones then re-run accesslint:diff to verify; for bulk work hand off to accesslint:audit.

3. Tear down

npx -y @accesslint/chrome@latest stop --all  # skip if ensure reported "managed":false

Gotchas

• ensure always determines the port — never hardcode 9222.
• CLI exit 2 = bad URL or page never loaded; check the dev server.
• Stash mode: sleep 2 covers most HMR cases; if baseline looks identical to current, add --wait-for "<selector>".
• Branch mode: no HMR — CLI opens a fresh tab each run. --wait-for is the rebuild gate.
• Heavy DOM changes between runs cause selector drift — re-run with accesslint:scan for the full picture.

Limitations

• Use this skill only when the task clearly matches the scope described above.
• Do not treat the output as a substitute for environment-specific validation, testing, or expert review.
• Stop and ask for clarification if required inputs, permissions, safety boundaries, or success criteria are missing.