Bionic Reader

Bionic reading for any website or PDF, bolds the first part of each word to guide your eyes and help you read faster. Available for Firefox and Chrome.

Install

• Firefox: Firefox Add-ons
• Chrome: Chrome Web Store (Coming soon. In the meantine load manually)

Features

• Toggle bionic reading on any website from the toolbar button or a keyboard shortcut (Ctrl+Alt+B on Firefox, Alt+Shift+B on Chrome, both customizable).
• Three fixation strengths: Low, Medium, High.
• A built-in PDF reader: read PDFs with bionic emphasis while keeping the page's original layout, images, and figures, or turn bionic off for the exact original page. A reflow mode is also available for a clean single-column read.
• Unicode-aware: keeps contractions intact (don't, it's) and leaves numbers unbolded.
• 100% local. Your pages and files never leave your device.

How it works

Bionic reading highlights the leading letters of each word so your eyes can move faster while your brain fills in the rest. On web pages, the extension restyles text in place. For PDFs, it uses a bundled copy of pdf.js to render the page and lay bionic text over it, so images and layout are preserved.

Privacy

Bionic Reader collects, stores, and transmits no data. Everything happens locally in your browser. See PRIVACY.md.

Building from source

Everything is shared between the Firefox and Chrome builds except the manifest. The two manifests live in manifests/ (manifest.firefox.json is Manifest V2, manifest.chrome.json is Manifest V3); build.sh selects the right one.

Requirements

• A Linux or macOS shell (or Windows with WSL / Git Bash), build.sh is bash.
• Node.js 18+ and npm (verified with Node 22.x).
• The zip command-line utility.
• Network access to npm (to download pdfjs-dist).

Build

./build.sh firefox    # -> dist/firefox/ + bionic-reader-firefox.zip  (Manifest V2)
./build.sh chrome     # -> dist/chrome/  + bionic-reader-chrome.zip   (Manifest V3)

Each run downloads pdfjs-dist@4.10.38 from npm, copies the matching manifest plus the shared source and the pdf.js library into dist/<target>/, and zips it with manifest.json at the archive root.

What is and isn't generated

• Hand-written source (no build step, copied verbatim): the two manifests, content.*, background.js, popup.*, viewer.*, and icons/icon.svg.
• Third-party library: pdfjs/pdf.mjs and pdfjs/pdf.worker.mjs are the official, unmodified, non-minified build of pdfjs-dist@4.10.38 from npm (reproduce with npm pack pdfjs-dist@4.10.38).
• Icons: the PNGs are exported from icons/icon.svg with any SVG rasterizer.

Loading unpacked (for development)

• Firefox: about:debugging#/runtime/this-firefox -> Load Temporary Add-on -> pick dist/firefox/manifest.json.
• Chrome: chrome://extensions -> enable Developer mode -> Load unpacked -> pick the dist/chrome folder.

License

MIT — see LICENSE. You're free to view, fork, modify, and use this code for any purpose, including commercial — just keep the copyright notice and license text from the LICENSE file in any copies or derivatives. If you build something interesting on top of it, I'd love to hear about it via my GitHub profile.

Acknowledgements

PDF rendering is powered by pdf.js, Mozilla's open-source PDF library, bundled unmodified. Inspired by the "bionic reading" idea of emphasizing the start of each word to guide the eye.

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© 2026 Jamil M. Licensed under MIT.