What makes the best coffee rating app useful

You can test a coffee rating app on four points before you commit to it: how fast it logs a cup, what its scores measure, how many ratings stand behind a number, and how it pays for itself.

Logging speed decides whether you keep using it

In Phillippa Lally's 2010 habit study at University College London, a daily behavior took 66 days on average to become automatic. Missing one day had little effect, but missing many lowered how automatic the habit became. An app that takes a minute and six screens to log a cup gets skipped on busy mornings, and every skipped morning slows the habit.

Time yourself logging a cup in any app you're trying. If it takes longer than finishing an espresso, you'll be tempted to skip it.

Score the drink, not the café

A star rating on a map app covers the whole visit. Service, seating and parking all land in the same number as the coffee. The numbers also bunch at the top: Nan Hu, Paul Pavlou and Jie Zhang found that 78% of Amazon book ratings were four stars or higher, because people with middling opinions tend not to post. The authors recommend looking at the spread of ratings along with the average.

A score tied to one drink at one café on one day gives you something you can compare. After a few dozen of them you can see whether a café's cortado scores higher than its drip, which tells you what to order there.

Count the ratings behind the number

An average built on three ratings moves a lot with each new one. If a café has three ratings averaging 7 and someone logs a 9, the average jumps to 7.5. With 300 ratings averaging 7, the same 9 moves it to 7.007. Look for an app that shows how many ratings make up a score, and treat a high average from three people as a lead, not a verdict.

Ask how the app makes money

A free app pays for itself through ads, data, subscriptions or business accounts. Each model is fine as long as you know which one it uses. If a business can pay for placement, the app should label paid placement where you see it.

What Jittr does

Jittr is a free iPhone app built around the drink. You score a cup from 1 to 10, add a photo, tag the flavors and attach it to the café, and the app fills in the café's city, state and metro area so the score counts toward local rankings. Each drink can carry tags for brew method, size and caffeine. The café rankings weight recent ratings more than old ones, so a café that changes roasters or staff shows it in the rankings. Your history is searchable, and you can follow friends and see their check-ins in a feed. There's a separate flow for rating bags of beans. Café owners can claim their café's profile, and premium business accounts are available.

A short checklist for any app

• How long does it take to log one cup?
• Does it score individual drinks or whole cafés?
• Can you see how many ratings sit behind a score?
• Do recent ratings count for more than old ones?
• How does it make money, and is paid placement labeled?
• Can you search your own history?