The 100ms Rule: Why Every Action in Vimcal Has to Feel Instant

TLDR: The 100ms rule says every interaction in an app should respond in under 100 milliseconds, because that's the point where it feels instant.

It goes back to Paul Buchheit, who created Gmail, and Superhuman made it famous for email.

Vimcal holds itself to the same rule for everything you do in your calendar: opening an event, switching weeks, finding times, sending availability.

Where the 100ms rule comes from

When Paul Buchheit built Gmail, he had a simple rule: every interaction should be faster than 100 milliseconds.

The number comes from decades of research on response times. Around a tenth of a second, a response feels instant.

Around one second, you notice the wait but keep your train of thought. Past ten seconds, your attention is gone.

Superhuman took Buchheit's rule and built a whole email client around it. Over time they pushed it even further, aiming for 50ms and then faster still.

The idea behind both is the same. When software responds instantly, it feels like an extension of what you were already doing.

Why speed matters more in a calendar than almost anywhere else

You don't use your calendar once a day. You touch it dozens of times: checking what's next, moving a meeting, finding a time for someone, looking up when a coworker is free.

A lot of those moments happen in the two minutes before a call, when you have no patience for a spinner.

A half-second delay doesn't sound like much. Multiply it by every click, every day, and it becomes the reason people put off scheduling until "later." Later usually means the thread goes cold.

Slow calendars also change how you work. You stop exploring options and settle for the first time that looks okay, because checking another one costs too much.

How we apply it at Vimcal

We hold every interaction to the 100ms rule, including the small ones.

• Opening an event
• Switching days, weeks, and months
• Finding open times and sending them to someone
• Searching your calendar
• Checking a coworker's availability
• Creating an event by typing it in plain English

If something can't be made to feel instant, we keep working on it until it does. Speed is a rule we build everything around, starting with the first version of a feature.

Keyboard shortcuts are part of the same idea. The fastest click is the one you don't have to make, so nearly every action in Vimcal has a shortcut.

What it feels like

The best compliment we get is when people stop noticing the calendar at all.

You think "move this to Thursday," and it's on Thursday. You think "when is Sarah free," and you're looking at Sarah's week. There's no gap between deciding and doing.

Once you've used software like that, going back to a slow calendar feels like wading through mud.

How to test any calendar's speed yourself

You don't need special tools. Open the calendar you use today and try these five things:

• Switch to next week. Does it appear immediately, or do events load in?
• Open an event. Is the detail view there the instant you click?
• Search for a meeting from last month. How long until you see results?
• Find three open times and send them to someone. How many steps did it take?
• Check when a coworker is free. Can you do it without leaving what you're doing?

If you notice a pause on any of these, you'll notice it hundreds of times a week.

FAQ

What is the 100ms rule?

It's the principle that every interaction in software should respond in under 100 milliseconds, the point where people perceive it as instant. Gmail creator Paul Buchheit used it, and Superhuman built its product around it.

Who came up with the 100ms rule?

Paul Buchheit, who created Gmail, is credited with applying it to product development. It builds on older research showing that responses under about a tenth of a second feel instantaneous.

What is the fastest calendar app?

Vimcal is built around the 100ms rule, so every action is designed to feel instant, and nearly everything has a keyboard shortcut.

Why does calendar speed matter?

Because you use your calendar dozens of times a day. Small delays add up, and they make people put off scheduling.

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