Check Diff Mode

herald check --diff (v0.4)

Status: planned / pre-release. This wiki page mirrors docs/ and documents the intended API of next-herald. Nothing is published yet; names may change before v1.0. See ROADMAP.

Compare SEO output against a base build or branch and report only what changed, for PR comments (#61).

herald check --build --snapshot .herald/snapshot.json               # on main: save a snapshot
herald check --build --diff .herald/snapshot.json --format markdown  # on a PR: compare with a file
herald check --build --diff origin/main --format sarif               # or with a git ref

• Snapshot: deterministic JSON per URL (status, title, description, canonical, robots, hreflang, JSON-LD types) plus the sitemap URL set.
• Git ref: the base is built in a temporary git worktree with node:child_process and removed afterwards. No dependencies (ADR 0002).
• Output: --format markdown (PR-comment summary, per-URL details collapsed, length capped), sarif (2.1.0, #34), plus pretty, json, github.
• Exit code: 1 only if a diff finding is error; normal rules are not reported in diff mode.

Diff rules

ID	Severity	What it reports
diff-noindex-added	error	URL indexable in base is noindex now
diff-canonical-changed	warn	Canonical target changed
diff-sitemap-url-removed	warn	URL in base sitemap missing now
diff-status-changed	warn	HTTP status changed (e.g. 200 → 404)
diff-title-changed	info	Title changed
diff-description-changed	info	Description changed

GitHub Actions

- run: npx herald check --build --diff origin/${{ github.base_ref }} --format markdown > herald-diff.md

Post herald-diff.md with your PR-comment step of choice. See CLI.