Dark mode for every PDF you read.
Online PDFs, offline PDFs, files straight off your disk. Dial in exactly how dark you want the page, then switch to Sepia or AMOLED when your eyes ask for it.
Free to install. Pro unlocks with a one-time $9.99 licence.
Visual Fatigue in Extended Screen Reading
Abstract
Prolonged exposure to high-luminance documents is associated with measurable increases in reported ocular discomfort. We examine reading sessions exceeding ninety minutes across 214 participants and find that perceived strain correlates more strongly with background luminance than with total session duration.
1. Introduction
Document formats designed for print carry an implicit assumption: that the page reflects light rather than emitting it. On a backlit display this inverts the ergonomics entirely.
Drag the handle — this is the extension's real overlay, running live.
Tune it until it's comfortable.
A clean inversion that keeps figures and diagrams legible. Adjust the darkness and contrast until the page sits right for your screen.
These are the extension's own controls, with the same ranges and the same rendering path. What you set here is what you'd see on a real document.
Legibility Under Reduced Luminance
The relationship between contrast ratio and sustained reading comfort is not linear. Below a certain threshold, increasing contrast produces sharper glyph edges but also raises the perceived intensity of the background field, which participants consistently described as harsh rather than crisp.
4.2 Method
Each participant read two documents of comparable length and typographic density. Luminance was held constant within a session and varied between sessions, counterbalanced across the cohort to control for order effects.
Built for people who read for hours.
Students, researchers, and developers living inside documentation. Everything below is in the extension today — the Pro items unlock with a licence key.
One-key dark mode
FreeFlip any PDF with Ctrl/⌘ + Shift + 1 or the toolbar button. No page reload, no re-render.
Darkness & contrast
FreeTwo sliders, not a single on/off switch. Soften the inversion on scanned pages, push contrast on faint text.
Online and offline
FreeWorks on PDFs on the web and on file:// documents opened straight from your machine.
Sepia & AMOLED
ProA warm paper-like tint for long sessions, and a deeper low-brightness mode built for OLED panels.
Per-site rules
ProAlways on for arXiv, never on for the one viewer that renders badly. Set rules per hostname and forget about them.
Overlay area control
ProTrim the overlay away from toolbars and sidebars — and save that layout per site so it sticks.
One price. Paid once.
The core reader is free forever. Pro is a single payment that never renews.
Free
- Dark mode on any PDF
- Darkness & contrast sliders
- Online & offline PDFs
- Keyboard shortcut
- Sepia & AMOLED modes
- Per-site rules
Lifetime
- Everything in Free
- Sepia reading mode
- AMOLED reading mode
- Per-site allow & block rules
- Saved overlay area per site
- Every future Pro feature
Secure checkout via Lemon Squeezy · Licence key emailed instantly
Why there's no monthly plan
PDF Dark Mode draws an overlay on a page you already have open. There's no server rendering your documents, no account holding your files, no sync bill arriving every month. Nothing about this tool costs money to keep running.
Charging rent for that would be charging you for the privilege of continuing to use software that already works. So it's one payment — and every Pro feature added later is included, without an upgrade prompt.
Three steps, about a minute.
No account, no sign-in flow. Your licence key is the whole system.
Buy the licence
Checkout runs through Lemon Squeezy. Your key lands in your inbox as soon as the payment clears.
Open the extension
Click the PDF Dark Mode icon, then Have a license? Activate here under the Plan section.
Paste and activate
Drop the key in and hit Activate Pro. Sepia, AMOLED, and per-site rules unlock immediately.
Questions worth answering.
Is $9.99 really the only payment?
Yes. There is no renewal, no expiry date, and no upgrade tier waiting behind it. Pro features that ship in future versions are included in the same licence.
Do I need an account?
No. There's nothing to sign up for. Checkout gives you a licence key, you paste it into the extension, and that's the entire process.
Can I use my licence on more than one browser?
Activate the same key in the extension on each browser you read in. If an activation is refused because you've reached the limit on your key, email me and I'll sort it out.
Does it work on PDFs saved on my computer?
It does, but Chrome and Edge block extensions from local files by default. You'll need to switch on Allow access to file URLs — the help page walks through it with screenshots.
What does the extension do with my documents?
Nothing leaves your machine. The overlay is drawn locally over the page you're already viewing, and the usage counters stay on-device. Details are in the privacy policy.
If it's open source, why pay at all?
The whole extension is GPL-3.0 and the source is on GitHub — you're welcome to build it yourself. Paying for a licence is how the maintained, store-published version keeps getting worked on.
Can I get a refund?
Refund requests are reviewed case by case. If it isn't working the way you expected, get in touch before anything else — most problems turn out to be a settings fix. See the terms for the full policy.
Something broken, or an idea?
Bug reports and feature requests genuinely shape what gets built next.