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.

Read →
Sleep 6 min

The 2 p.m. Coffee Rule Is Thinner Than It Looks: 48 Nights of Sleep Improvement Data

For eleven years I did not drink coffee after 2 p.m. If you had asked me why, I'd have said it was the cheapest sleep improvement on offer: everyone knows caffeine has a long tail, everyone knows the…

Read →
Caffeine 6 min

Apple Watch Series 11, Six Weeks In: A Smartwatch Comparison That Only Cares About Sleep

The question I actually wanted answered was narrow, and I suspect it's yours too: can a $399 watch settle the argument I have with myself every afternoon about the 4 p.m. coffee?

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