A reading ruler that works on PDFs too.
The free reading-ruler extensions are small and well liked, and their reviews all ask for the same two things: work in PDF files, and keep working after the next update. ReadFocus has a ruler that follows your mouse, toggles with a shortcut, and since 0.2.0 runs on PDFs on the web. It is free, needs no account, and nothing leaves your browser.
Add to Chrome Add to Firefox Free to install. Also works in Edge from the Chrome Web Store.
Side by side
| ReadFocus | Reader Line | ReadingLine | ReadingRuler | |
|---|---|---|---|---|
| Price | Free (the ruler never costs anything); $12 once unlocks the rest | Free | Free | Free |
| Account or sign-in | No | Not shown on the listing | Not shown on the listing | Not shown on the listing |
| How the ruler moves | A soft band that follows the mouse | Follows the mouse; colour filters | Follows the mouse; "zero controls" (a review) | Follows the mouse; resizes to the text; colour picker |
| Keyboard toggle | Yes (Alt+Shift+R), and a switch in the popup | Not shown on the listing | Not shown on the listing | Reviews report trouble starting it with the shortcuts |
| PDF files | Yes, PDFs on the web: "Read this PDF" opens the file as real text in ReadFocus's own reader, ruler included (first page free; whole file with the unlock) | No — the top reviews all ask for it | No — a review asks for it | Not shown on the listing |
| Colour and size of the band | One band; no colour or size controls yet | Colour filters | None; a review says it is unusable on dark themes | Colour picker; a review says it forgets the colour |
| Goes with | Bold word starts, paragraph focus, bigger text, dyslexia-friendly fonts | Ruler only | Ruler only | Ruler only |
| Where it runs | Only on sites you switch it on for (asked once per site), then automatically | Not shown on the listing | Not shown on the listing | Reviews report it working on Google search but not other sites |
| Chrome Web Store rating when we looked | New — listed September 2026, no ratings yet | 4.9 ★ from 100 ratings, 20,000 users | 3.9 ★ from 32 ratings, 8,000 users | 3.4 ★ from 14 ratings, 722 users |
| Last update | October 2026 | December 2024 | June 2022 | April 2026 |
| What recent reviews report | — | "Hope it works in pdf soon"; otherwise does what it says | "Zero controls"; wish for colour, size and opacity | "Not working after recent update"; works on some sites only |
Rival facts as shown on their Chrome Web Store listings and reviews in September 2026; "not shown on the listing" means we could not confirm it either way. Tell us at info@gankdat.com if something here is out of date and we will fix it.
Why a ruler, and why ours
A reading ruler keeps your eyes on one line: the band moves with the mouse, the rest of the page stays as it is. People with ADHD or dyslexia, anyone reading long documents, and anyone presenting on a shared screen use one. The free ruler extensions do this well on ordinary pages. Where they stop is the PDF: the browser's PDF viewer draws pages as pictures, so a ruler extension cannot see the text. ReadFocus takes the other route — "Read this PDF" in the popup fetches the file and rebuilds each page as real paragraphs in ReadFocus's own reader, so the ruler, the bold word starts and the fonts work on it like on any web page. The first page is free so you can see it work; the unlock reads the whole file. PDFs stored on your computer are not supported yet.
If you only want a ruler and never read PDFs, Reader Line is a fine free choice and we say so. If you want the ruler on a toolkit that also bolds word starts and dims everything but the paragraph you are on, or you want it on PDFs, that is ReadFocus. For a broader accessibility suite with read-aloud, see Dyslexly or Helperbird; our reading-extension comparison covers them.
What ReadFocus's ruler does not do yet
- No colour, height or opacity controls — one soft band. Tell us if you need them.
- No locking the band in place to scroll under it; it follows the mouse.
- No PDFs stored on your own disk; PDFs on the web only.
- No Google Docs (Docs draws its text as graphics, so no extension of this kind can).
Free, forever
- The reading ruler, with its keyboard shortcut, on every site you switch it on for
- Bold word starts at three strengths, and bigger text
- The first page of any web PDF in the ReadFocus reader
Unlock — $12, once
- Precise bold strength and paragraph focus
- OpenDyslexic and Atkinson Hyperlegible fonts
- Whole PDFs, every page
- One key for every browser you sign in to; works offline; 14-day refund
Get your key — $12, once
Sold by our merchant of record (Stripe), which charges the right VAT for your country and
emails the key within a minute. Install the extension first, then paste the key.
More on the ReadFocus page · read the privacy policy.