Guardrail Blocks

Most accessibility failures on WordPress sites are authoring failures: a brand color that doesn’t meet WCAG contrast, a heading hierarchy scrambled by reordering, an accordion built from divs with no keyboard support. They look fine in the editor and fail the audit later.

Guardrail Blocks takes a different approach: instead of offering accessible options, its blocks make the failure impossible to author — and re-verify everything on every page view.

The guarantees

• WCAG-safe color contrast — Button backgrounds come only from your theme’s palette (plus any custom colors added in Global Styles), and the most readable text color is chosen automatically (the live ratio is shown in the sidebar, e.g. “Contrast 8.36:1 — AA ✓”). The pairing is re-validated server-side on every page view against your theme’s current palette, so switching themes or changing brand colors can never leave a failing button behind.
• Unbreakable heading hierarchy — There is no heading level control anywhere. An Accessible Heading derives its level (H2–H6) from how Accessible Sections are nested, and re-derives it when you reorder, nest, or un-nest — the document outline stays valid by construction. Card titles and accordion headers participate too, always one level below their section’s heading.
• Correct interactive semantics — The Accordion ships the full WAI-ARIA disclosure pattern: real buttons inside correctly-leveled headings, aria-expanded/aria-controls wiring, Enter/Space toggling, arrow-key navigation between headers, and content that stays reachable without JavaScript.
• Performance-correct media — The Media Figure renders through core’s responsive-image pipeline with explicit dimensions (no layout shift), srcset/sizes, a hero toggle for fetchpriority="high" (better LCP) vs. lazy loading, and alt text enforcement with editor warnings.

The blocks

Accessible Section, Accessible Heading, Accessible Button, Card + Card Grid, Accessible Accordion, Notice (info/success/warning/error with correct ARIA roles), Media Figure, and a Table of Contents that is generated from the page’s real outline on every view — it can never go stale.

Safety nets

• The Outline Checker panel (in the page sidebar) watches the whole document — including core Heading blocks — and flags skipped levels and extra H1s with one-click block selection.
• Everything inherits your theme’s colors, spacing, and typography via theme.json. Nothing fights your design.
• The plugin makes zero external requests and collects no data.

Source code & development

The compiled block scripts in build/ are generated with @wordpress/scripts (webpack). The complete, human-readable source code is included with this plugin in the src/ directory (TypeScript and SCSS, one folder per block). To rebuild build/ from it: npm install && npm run build (Node 22; package.json and tsconfig.json are included).

Development happens publicly at https://github.com/breonwilliams/guardrail-blocks, which also carries the full test suite (Jest, PHPUnit, Playwright) and CI.