A Field Guide — Issue №001
A Field Guide to Caffeine & Rest

Coffee you love.
Sleep you need.

Most advice treats them as enemies. We think they've just been badly introduced. JavaSleep is a slow magazine about the hours between your last sip and your first dream — with honest reviews, quiet science, and one very useful calculator.

Try the caffeine calculator → Read the field notes
— On what we do
We write for people who order a third espresso and mean to be in bed by eleven. Who know that a good night's sleep is half the pleasure of a good morning's coffee. We don't tell you to quit caffeine. We tell you when, and how much, and which cup is worth the trade.
Instrument №01 — The Caffeine Timeline

How much caffeine
will still be awake
at your bedtime?

Caffeine doesn't clock out when you do. It has a half-life of about five hours, which means your 3 PM latte is still at half strength when you're trying to fall asleep at 11. Here's the honest math.

Caffeine at bedtime
—mg
Calculating
Adjust the inputs above to see your personal timeline.
Field Notes — Recently Published

Three things worth reading slowly.

Editor's Pick 5 min

Best Travel CPAP Machines (2026): AirMini vs. Transcend Micro vs. Z2 Auto

The best travel CPAP machine for most people is still the ResMed AirMini — if you can tolerate its waterless humidification and proprietary tubing.

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Wearables 6 min

Samsung Galaxy Unpacked 2026 and the Number Nobody Put on a Slide

0.54. That is the highest specificity any of seven consumer sleep trackers managed in Chinoy et al. (2021), published in Sleep, when 34 healthy adults slept in a lab wearing the devices while…

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Sleep 6 min

Twenty-One Nights With the Samsung Galaxy Watch 9: Can a Wrist Sensor See Your 4 p.m. Coffee?

The Samsung Galaxy Watch 9 lists at $349 and lands near $130 if you have a dead watch in a drawer, which is how most people will end up buying it. I bought one for a narrower reason.

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Every issue →
“The most civilized thing a person can do is enjoy a cup of coffee at ten in the morning and still sleep at ten at night.
— Editor's Note, Issue №001