Building an image gallery slider with Swiper.js lets you create a visually appealing and interactive way for users to browse photos. Swiper's flexible markup makes it easy to separate your main gallery from a thumbnail navigation slider, so users can quickly jump to any image. Always use clear alt text for every image to support accessibility—this helps screen readers describe your gallery to visually impaired users.

When configuring your gallery, connect a main Swiper instance to a thumbnail Swiper using the thumbs module. This setup allows users to click on thumbnails to navigate the main gallery. Add Swiper's navigation controls, and ensure you provide aria-label attributes for better accessibility. For performance, optimize your images to be as small as possible while retaining quality, and use responsive CSS to adapt your gallery layout for different devices. Swiper's breakpoints make it simple to adjust the number of visible thumbnails on mobile versus desktop.

To further improve accessibility, enable Swiper's a11y module. This adds keyboard navigation, focus management, and helpful announcements for assistive technologies. For best results, test your gallery with a keyboard and screen reader.

By following these best practices, your Swiper-based image gallery will be both user-friendly and performant across devices.