HTML

HTML markup is validated against W3C standards for cross-browser compatibility.

Unnecessary code, comments, and debug elements are removed before deploying to production.

Custom elements must implement ARIA reflection via ElementInternals, keyboard interaction, and form association so that screen readers and assistive technologies can interpret them correctly.

A noscript tag provides fallback content for users with JavaScript disabled.

The HTML5 doctype declaration must appear as the first line of every HTML document to trigger standards mode rendering in all browsers.

All ID attributes are unique within the document. No duplicate IDs exist on the page.

A custom 404 error page is designed with helpful navigation options for lost users.

The dir attribute is used for languages that read right-to-left (RTL) or mixed content.

Forms provide clear validation feedback with accessible error messages and proper ARIA attributes.

Set the correct type attribute on input elements to trigger the right mobile keyboard, enable browser validation, and improve autofill accuracy.

File upload components are accessible with proper labels, file type restrictions, and progress feedback.

Search functionality is accessible with proper input type, label, role, and autocomplete suggestions.

Videos have captions, audio descriptions, transcripts, pause controls, and avoid autoplay for users with hearing, vision, or cognitive impairments.

HTML5 video elements should have a poster attribute providing a thumbnail image displayed before the video loads or is played.

The charset (UTF-8) is declared correctly as the first element in the head.

The viewport meta tag is declared correctly for responsive design.

The <html> element must have a lang attribute with a valid BCP 47 language code so screen readers, translation tools, and search engines know the primary language of the page.

All necessary favicon formats are implemented for browsers, devices, and PWA support.

Breadcrumb navigation is implemented with proper semantic markup and ARIA attributes for accessibility.

Pagination controls are accessible with proper ARIA labels, keyboard navigation, and current page indication.

Prevent JavaScript from blocking HTML parsing by using defer, async, or type=module attributes on script tags so the browser can continue building the DOM while scripts download.

Use Subresource Integrity (SRI) hash attributes on external scripts and stylesheets loaded from CDNs to ensure the content hasn't been tampered with.

HTML5 Semantic Elements are used appropriately (header, section, footer, main, article, aside...).

Include a Web App Manifest (manifest.json) linked from the HTML head to enable Progressive Web App features like home screen installation, standalone display, and splash screens.

The web app satisfies the browser's minimum PWA installability requirements: a valid web app manifest, a registered service worker, HTTPS, and maskable icons.