The Book Cover Maker is 100% client-side. Each element — the title, subtitle, author, blurb, a shape, a barcode placeholder or an uploaded photo — is a plain typed object held in the page, and a pure engine (bookCoverEngine) draws them onto an in-browser HTML5 <canvas>. When you upload a photo it is read straight into an in-memory Image with URL.createObjectURL and drawn on-device; the duotone and filter passes run locally with canvas getImageData and ctx.filter, so your image is never sent anywhere. There is no stock-image library and no AI generation — you bring your own photo, and the other backgrounds are CSS/SVG gradients, procedural patterns and duotones generated in-browser. Export renders the same scene to a canvas at print resolution and saves it with canvas.toBlob, so every file is produced on your device. The only optional network use is consent-gated ads; everything else works offline once the page is cached.

The spine is only as thick as the paper stack, so its width is the interior page count multiplied by the thickness of one leaf of paper. This tool uses the standard Amazon KDP values: 0.002252 inches per page for white or premium-colour paper, 0.0025 inches for cream, and 0.0032 inches for standard colour. For example, a 300-page white-paper book has a spine of 300 × 0.002252 = 0.676 inches (about 203 pixels at 300 DPI). The full wrap width is then two trim widths plus the spine plus 0.125 inches of bleed on each outer edge, and the height is the trim height plus 0.125 inches top and bottom. The tool shows the computed spine in inches and pixels live as you change the page count and paper type. Because printers round differently and KDP requires 79+ pages before you can add spine text, always confirm the exact spine, trim and bleed with your printer or download their template before sending a print file.

For an ebook, Amazon Kindle recommends a portrait cover with a height-to-width ratio of about 1.6:1 and an ideal size near 1600×2560 pixels, which this tool ships as a dedicated preset. Exporting at 2560 pixels tall keeps the cover crisp at thumbnail and full size and satisfies KDP’s minimum and recommended dimensions in one file, in the sRGB colour space. Real print trim sizes such as 6×9, 5×8, 5.5×8.5 and A5 are also available if you are designing the front of a paperback. The tool exports a flat RGB raster (PNG or JPEG), not a print-ready CMYK PDF — that is perfect for ebooks and mockups, but for a professional print run you convert colour and flatten in a prepress tool.

Full Wrap mode lays out the back cover, spine and front cover as one print canvas. The front and back are full layer regions where you composite editable text, shapes, uploaded photos and a barcode placeholder (a white quiet-zone box where KDP prints the real ISBN barcode). The spine is a structured element: type a spine title and author and the engine auto-fits them as vertical text, reading up or down, sized to the computed spine width, with an optional solid spine colour. The canvas adds 0.125-inch bleed on every outer edge and shows teal trim lines, gold safe-margin insets and spine fold lines as on-screen guides that are never baked into the exported file. Export the whole wrap as a PNG or JPEG at 150 DPI (screen mockup) or 300 DPI (print quality). It is a faithful mockup and a strong starting file, but confirm exact specs with your printer before final upload.