Aims to be the biggest checklist of inclusive design considerations ever. Includes items for accessibility, performance, device support, interoperability, and language. Pull requests welcome!

• Minify CSS and JS, and remove unused/redundant code
• Use screen reader and keyboard accessible HTML
• Compress raster images
• Optimize SVG path data
• Make sure heading levels describe a logical section/subsection structure
• Only include heading elements where they introduce sections of content
• Remove potentially insensitive or uninclusive language (use 'singular they')
• Give video content captions and transcripts
• Make sure main body (paragraph) text is no smaller than the default (user agent) size
• Support 'pinch zoom' (remove user-scalable=no if present)
• Use relative units (em, rem, and ch), especially for font metrics
• Make sure styles and scripts are not render blocking
• Install a service worker and cache all applicable assets
• Use content-based, not device-specific, media queries
• Provide alternatives and/or descriptions for complex visualizations
• Include only clear, meaningful animations
• Make sure controls do not elicit unexpected or jarring behavior
• Do not include third parties that compromise user privacy
• Do not recreate supported and expected browser behaviors with bespoke scripts
• Support Windows high contrast mode (use images, not background images, if salient)
• Provide alternative text for salient images
• Apply alt="" or aria-hidden="true" to decorative images
• Make sure text and background colors contrast sufficiently
• Provide <title>s that name the site and the specific page
• Provide large touch 'targets' for interactive elements
• Use data tables (<table>) for data, not layout
• Make scrollable elements focusable for keyboard users
• Do not rely on color for differentation of visual elements
• Use the same design patterns to solve the same problems
• Ensure keyboard focus order matches visual layout
• Lazy load large image assets
• Translate / spell out acronyms the first time you use them
• Do not hijack standard scrolling behavior
• Move focus between dialogs and the controls that invoked them
• Give all form elements permanently visible labels
• Give grouped form elements group labels
• Provide status and error messages as WAI-ARIA live regions
• Provide clear, unambiguous focus styles
• Employ well-balanced, highly legible fonts (not too complex or elaborate)
• Do not use very thin font faces
• Ensure states (pressed, expanded, invalid, etc) are communicated to assistive software
• When component behaviour changes across breakpoints, ensure its presentation and state are described differently to assistive software
• Provide a default language and use lang="[ISO code]" for subsections in different languages
• Make controls look like controls; give them strong perceived affordance
• Underline links — at least in body copy
• Make sure all content belongs to a landmark element (<header>, <footer>, <nav>, <main>, etc)
• In visual designs, avoid pure white or pure black
• Mark invalid fields clearly and provide associated error messages
• Ensure content is not obscured through zooming (no fixed widths)
• Provide a manifest.json file for identifiable homescreen entries
• Indicate swipe gesture support clearly, and provide simple tap-based alternatives
• Make sure data tables wider than their container can be scrolled horizontally
• Avoid time constraints where possible; provide a clear warning and option to extend where not possible
• Label and describe the same things with the same terminology
• Ensure disabled controls are not focusable
• Do not instate 'infinite scroll' by default; provide buttons to load more items
• Avoid justified body text
• Provide enough spacing between lines of text (line-height)
• Ensure content is accessible when printed out our saved as PDF.
• Provide a skip link if necessary
• Avoid all-caps text
• Ensure that content is written as clearly and simply as possible
• Provide descriptive captions for figures
• Warn users of links that have unusual behaviors, like linking off-site, or loading a new tab
• Make content easier to find and improve search results with structured data
• Use textual labels to make voice activation cues obvious
• Do not mark up subheadings / straplines with separate heading elements