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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Caffeine 7 min

Vagus Nerve Stimulation vs. a 4 p.m. Espresso: Twenty-One Nights, One Ear Clip, and a Sleep Tracker

For twenty-one nights I ran a 4 p.m. double espresso against a clip on my left ear, because the consumer pitch for vagus nerve stimulation — that a small current at the right patch of cartilage can…

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Wearables 10 min

Casio Wearables vs. the 2 p.m. Coffee Rule: 31 Nights With a Retro Ring and Two Step-Counting Digitals

The three Casio wearables I bought for this piece cost ¥52,000 before a forwarding service in Chiba charged me another ¥5,800 to put them in an envelope.

Read →
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