Bionic Reading Converter

What Load sample turns into

Load sample fills the box with a 77-word note about a support worker named Marta and her paper call log. At the default Medium strength, the first sentence reads:

The counter under the preview shows 77 words with 76 bolded. The odd one out is the digit 3 in "caught 3 refunds". Numbers stay plain on purpose, since a half-bold figure such as 1250 reads like a typo. Across the passage, 40 percent of all letters end up bold.

Switch Bold to Every 2nd word and the same passage drops to 38 bolded words and 19 percent of letters in bold:

Readers who find full bionic text busy often settle here. The page stops looking like a ransom note, and the eye still gets an anchor every other word.

How much of each word turns bold

The rule is simple arithmetic. Take the word's letter count, multiply by the strength, round to the nearest whole letter, and bold at least one. Light uses 20 percent, Soft 30, Medium 40, Firm 50 and Heavy 60.

A few details decide what counts as a word:

• Contractions stay whole. Caller's and don't are one word each, and the apostrophe counts toward the length.
• Hyphens split. Well-known becomes two words, well and known, so each half gets its own anchor.
• Accents count as one letter. Café is four letters, and the bold never cuts an accent off its letter.
• Punctuation and spacing pass through. Line breaks and blank lines in your paste survive into the preview and every export.

Bionic Reading is a registered trademark of Bionic Reading AG, the Swiss company behind the original app. Their exact bolding table is not public. The rule above is ours, so output here and in their app differ on some words.

Does bionic reading make you read faster?

Swiss typographer Renato Casutt designed the method, and the format went viral on TikTok and X in 2022 with claims of reading twice as fast. The tests run since then point the other way.

• Readwise, 2022. The reading app ran an open online test with about 2,000 readers, timing each person on plain and bolded passages. Average speed showed no meaningful difference.
• Vrije Universiteit Amsterdam, 2024. Reading researcher Jonathan Snell measured reading times on bionic and plain text in controlled experiments and found no speed benefit from the bolding.

Eye-movement research explains the result. When you read, your eyes stop on a word for about a quarter of a second, then jump ahead 7 to 9 letters. Skilled readers already land near the middle of each word and predict short words without fixating on them. Bold word starts do not change where the eye lands enough to cut the number of stops.

Run a fair test on yourself

A careless test flatters whichever version you read second. Rereading is faster, and the second passage feels easier once you are warmed up. This routine controls for both:

1. Pick two passages of similar difficulty, about 300 words each. Two neighboring sections of one book chapter work well.
2. Paste the first passage, set the preview to Plain, press Start timed read, and stop on the last word.
3. Close the page, write down three facts from the passage, and check them. Speed without recall is skimming.
4. Paste the second passage, switch to Bionic, and repeat both steps.
5. The next day, run two fresh passages in the opposite order.

For reference, a 2019 review of 190 reading studies by Marc Brysbaert put average silent reading for English adults at 238 words per minute for non-fiction and 260 for fiction. A gap under 10 percent between your two runs is inside normal day-to-day noise. Look for a bigger gap across several sessions before switching formats for good.

Which copy button fits where you paste

Markdown bold works mid-word because CommonMark allows asterisk emphasis inside a word. Underscores do not, which is why the export never uses __. To get a PDF, open the downloaded file in your browser and print to PDF.

Use Unicode bold sparingly. Those letters are separate symbols, not formatted text. Screen readers spell them out or skip them, platform search does not match them, and only plain A to Z and digits have bold forms, so an é stays regular. Fine for a bio line, poor for a whole post.

Settings worth trying

• Dim the unbolded part greys the word endings so the anchors stand out more. On a bright monitor this helps. On e-ink or a phone in sunlight, the lower contrast makes text harder to read, so leave the box unchecked there.
• Serif suits long reading on large screens. Bold serif starts look heavier than sans serif ones, so pair Serif with Soft or Medium strength.
• Heavy bolds most of every word and flattens the contrast the format depends on. Above Firm, most readers see a wall of bold.

The tool remembers your strength, font, size and dim choices in this browser for your next visit.

Where this converter falls short

• Scripts without spaces. Chinese, Japanese and Thai run words together, so a whole sentence counts as one word and gets one bold start. The format has no useful result there.
• Arabic and other joined scripts. A weight change in the middle of a word breaks letter joins in some fonts. Check the preview before sharing.
• Plain text in, plain text out. Headings, links and lists in your paste arrive as plain lines. For a PDF or EPUB, copy the text out first.
• Long pastes. Past 40,000 characters, about 6,500 words, the preview waits for a pause in typing before updating.
• Not the official app. If you need output matching the Bionic Reading app or its browser extension word for word, use theirs.

Conversion runs in your browser. Your text never reaches Toolexe, and a page refresh wipes the box.