Saccade

A kinder way to read PDFs on Linux.

Some of us lose the line halfway through a paragraph. Some of us read the same sentence three times and still take nothing in. Saccade is a PDF reader built around that.

It uses bionic reading: the first few letters of every word are bolded, so your eye lands on a fixation point instead of hunting for one, and the rest of the word is filled in almost without effort. How much gets bolded is up to you, and it switches off with one key if you would rather compare. On top of that you can set the spacing and size that actually suit you, and dim everything except the paragraph you are on.

It is named after saccades — the small, quick jumps your eyes make as you read.

Maths gets particular care. Copying a formula out of a PDF usually gives you nonsense, because a PDF stores placed glyphs rather than equations. Saccade instead shows each formula exactly as the book prints it — fraction bars, roots, limits and big operators intact — in the colours of whatever theme you are reading in.

Saccade is in beta (0.9). If something reads badly, please tell me in Issues — a screenshot and the book's name is plenty.

Makes the words easier to take in

• Bionic fixations: bolds the first part of every word, and you decide how much (20–80%), or turn it off with Ctrl+B
• Focus mode (F2) dims every paragraph except the one you are reading; it follows your pointer, so there is nothing to learn
• Easy-reading setup — one menu item, and the text gets bigger, the line shorter, the spacing wider and the page warmer. Reset reading settings puts everything back, so it is safe to experiment
• Line, letter and word spacing, and column width, all adjustable. Wider letter spacing is one of the few things with real evidence behind it for dyslexic readers
• Fonts made for easier reading — OpenDyslexic, Atkinson Hyperlegible, Lexend — appear at the top of the font list when you have them installed (Help → Reading fonts shows how to get them)
• Five colour themes, from warm paper to night, plus a zen mode (F11) that hides everything but the words

Keeps your book a book

• Text re-flows into a comfortable column, but headings stay headings, bold stays bold, and footnote markers stay where they belong
• Formulas are shown as the book prints them — fractions with their bars, roots, limits, big operators — instead of the scrambled text you get from copying maths out of a PDF
• Scanned books are shown as the scanned page, because their hidden OCR text turns k ∈ ℤ₊ into k E Z+
• The contents pages inside a book are clickable, and so is the chapter list in the sidebar
• Bookmarks, full-book search, and it remembers the page you stopped on

No terminal, no Python, no coding. Go to the Releases page and download the file for your system:

• Debian, Ubuntu, Linux Mint and similar — download the .deb file and double-click it to install. If your file manager does not offer to install it, open a terminal in the download folder and run:

  sudo apt install ./saccade_*_all.deb

• Any other Linux distro — download the .AppImage file, right-click it and tick "Allow executing as program" (or run chmod +x Saccade-*.AppImage in a terminal), then double-click it to run. It carries its own Qt and PyMuPDF, so there is nothing else to install.
• Arch Linux — see the AUR instructions below.

Once it is on the AUR, any helper will do:

yay -S saccade

Or build it yourself from this repository:

cd packaging/aur
makepkg -si

Before uploading to the AUR: tag a v0.9.1 release, put the release tarball's real checksum in sha256sums (makepkg -g prints it), then regenerate .SRCINFO with makepkg --printsrcinfo > .SRCINFO.

For developers: you need Linux, Python 3.9 or newer, PyQt6 and PyMuPDF. The last two install themselves with the app.

git clone https://github.com/khodekia/saccade.git
cd saccade
python3 -m venv .venv
.venv/bin/pip install .
.venv/bin/saccade

While hacking on it, run it straight from the checkout instead:

.venv/bin/python -m saccade

bash packaging/build_deb.sh
sudo apt install ./packaging/dist/saccade_*_all.deb

bash packaging/build_appimage.sh
./packaging/dist/Saccade-<version>-x86_64.AppImage

The AppImage build downloads appimagetool once.

1. Drop a PDF onto the window, or press Ctrl+O.
2. Drag the slider to taste; Ctrl+B turns the bolding off and on so you can compare.
3. N and B turn pages (PgDown/PgUp work too). Space scrolls and moves on at the end of a page. Type a page number in the toolbar to jump.
4. Ctrl+F searches the whole book; hits appear in the Results tab.
5. Ctrl+D bookmarks the page you are on.
6. The View menu holds the easy-reading setup, focus mode, themes, sizes and spacing.

F1 lists every shortcut.

If a book opens as a wall of nonsense, it is probably a scan — run OCR on it first (ocrmypdf in.pdf out.pdf) and it will behave.

.venv/bin/python -m unittest discover -s tests -t .
.venv/bin/python tools/smoke_gui.py     # drives the real window, headless

saccade/
  bionic.py      # the fixation algorithm: word -> HTML with bold openings
  document.py    # PDF backends, text extraction, outline, formula crops
  layout.py      # page rendering: structured flow, formulas, page-layout mode
  settings.py    # everything that is remembered between sessions
  support.py     # donation wallets, repo link, bundled icons
  theme.py       # reading themes and the application's own styling
  app.py         # start-up and the command line
  ui/
    main_window.py  # window, toolbar, menus, shortcuts
    reader_view.py  # the reading surface itself
    about_dialog.py # this app's About box
    sidebar.py      # chapters, bookmarks, search results
    search.py       # full-book search, off the main thread
packaging/       # .deb, AppImage and AUR recipes
tools/           # headless checks that drive the real window
tests/           # unit tests for the algorithm, the PDF layer and search

If Saccade makes your reading easier and you feel like buying me a coffee:

Bitcoin (BTC) — BTC network

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Ethereum (ETH) — ETH network

0x1808eA06242729efA2E5a7B9c212530169011392

USDC — Ethereum network

0x1808eA06242729efA2E5a7B9c212530169011392

Dogecoin (DOGE) — Doge network

DGfQtSnAgqBXzeuyQSmKLeMgaiVT5Rt1pT

Toncoin — TON network

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No pressure at all — the app is free either way, and always will be.

MIT, see LICENSE. The bionic-reading idea was popularised by Renato Casutt.