Use Bionic Reading as a focus aid, not a speed hack

The pitch is that bolding the front of every word makes you read faster. The largest open community test of that claim, run by Readwise on 2,074 readers in 2022, found the opposite: with Bionic Reading turned on, the average reading speed dropped from 327.9 to 325.3 words per minute. Comprehension was identical at 88% either way. A 2024 paper in Acta Psychologica lands on the same result and titles itself, plainly, "No, Bionic Reading does not work."

So the speed claim is dead. And yet about 52% of readers in that same Readwise dataset did get faster with the formatting on, by an average of 35 WPM. Roughly the other half got slower by a similar amount. That split is the most useful sentence anyone has written about Bionic Reading. The interesting question isn't whether it works. It's whether it works for you, and for what.

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What the formatting actually does

The mechanic is simple. Each word is split at a fixation point, usually the first 2 to 3 letters, and the front portion is bolded. Your eyes land on the bold anchors, and your brain is supposed to fill in the rest without slowing down to spell it out. Z.Tools' converter exposes a fixation slider from 1 to 5 and an optional gradient mode that fades the bold weight from heavy to medium across the highlighted letters, so the contrast feels softer over a long page.

Under the hood, the converter uses an open-source library called text-vide. That library is MIT-licensed and was originally published as bionic-reading on npm before being renamed to avoid the Bionic Reading trademark, which is held by Switzerland-based BRCG Casutt GmbH. The output is functionally the same; the legal status is what changed.

The marketing says faster. The data says about half the time.

Readwise's June 2022 test is the largest public dataset on this question. Participants read two 1,000-word essays by Paul Graham, each split into four chunks that alternated between Bionic and plain formatting. After cleaning the data, the analyzed sample was 1,916 readers. The average dropped 0.8% on Bionic, a tiny difference that wasn't statistically significant (p = 0.055). Comprehension didn't move. The result that got buried under the headline was the individual variance: 52% of readers were faster with the formatting on, with average gains of about 35 WPM, and 48% were slower, by about 43 WPM. Bigger swings in either direction were common.

The 2024 Acta Psychologica paper went further. After a controlled lab experiment, the authors concluded there is no measurable benefit at the population level and no eye-tracking evidence that Bionic Reading reduces fixation duration or saccade length, which would have been the mechanism by which faster reading could happen. A 2025 eye-tracking study from researchers at the University of Ljubljana, published in SAGE Open, found similar results across screen and print, with usability ratings that were politely lukewarm.

If the marketing claim is "this will make you faster," the answer from the strongest available evidence is that, in expectation, it won't. The product page tends not to mention this.

Where it does seem to help

The interesting research is the opposite of what the marketing promises. A 2023 classroom study with 10th-grade students reported gains in self-reported engagement and motivation, not raw reading speed. Education researchers working with students who have learning disabilities have flagged Bionic-style formatting as a low-cost intervention that some readers stick with, especially when the alternative is bouncing off the page entirely. ADHD-focused communities have been doing this informally for years; readers describe the formatting as a kind of visual handrail that keeps the eye from drifting off mid-sentence.

None of those are speed claims. They're focus and adherence claims. And they make sense if you take the formatting at face value: it's a typographic prosthetic that increases visual contrast inside every word. If contrast helps your attention, you stay on the page longer. If it doesn't, you don't. There's no version of this where the trick is universal.

A 60-second self-test

You don't need a paper to know whether you're in the half that benefits. Try this:

1. Pick a 1,500-word article you actually want to read. Long enough that focus matters, not so long that you'll abandon it.
2. Paste the first half into the converter at fixation 3, gradient on. Read it on the page, timing yourself.
3. Read the second half as plain text from the original source. Time that too.
4. Ask yourself two honest questions before checking the numbers: which half did you actually finish? And on which half did your eye drift the least?

If your gut answer is "the Bionic half kept me on the page," the WPM number doesn't matter much. You found the version of this tool that's worth keeping. If the answer is "they felt the same" or "the bold annoyed me," that's also useful, and you can close the tab and move on. About half of testers land in each camp; nobody is wrong for being in either one.

Settings that are actually worth tuning

Two controls do almost all the work. Fixation point is the only setting most people need to think about: 2 produces a barely-there nudge that's easy to read continuously, 3 is the default and usually a fine starting point, and 4 or 5 produce heavy bolding that suits dense academic prose more than blog posts. The gradient toggle matters more than people expect: with it off, every bolded character is full weight, and a long page can feel visually loud after a few minutes. With it on, the weight tapers from 700 to 500 across the bolded letters, which softens the rhythm enough to sustain a 20-minute read.

What to actually take away

Bionic Reading isn't a speed hack and the strongest evidence on the question now says so explicitly. It's a typography toggle that helps roughly half the people who try it stay on the page, and helps a smaller minority focus considerably better. That's a real benefit, just a different one from what the original pitch claimed. Use it on the long-form article you keep meaning to read instead of the listicle you'd skim either way. Run the 60-second test once. Believe the result, even if it's "no thanks."

Z.Tools·z.tools

Bionic Reading Converter · Z.Tools

Bold word beginnings to boost reading speed and focus