AI nutrition coach
Every calorie app is guessing. This one finds out.
Photograph your food. Step on the scale. Marble works out what you actually burn — and corrects the target it gave you on day one.
The scale
Your scale lies. Every morning.
The correction
Two weeks in, it tells you it was wrong.
- Planned
- −1.1 lb / wk
- Measured
- —
- Weigh-ins
- 1
Day one. The target is arithmetic, and arithmetic can be wrong.
It moves half the gap, never more than 250 calories at once, then waits another fortnight before it touches the number again.
The app
Three screens. Nothing to learn.
What's left, and what you ate. One timescale, no streak to protect.
Where the number starts
We show you the shaky line.
What it asks of you
Nothing, to begin with.
- No account
- No email
- No permissions on first launch
- Weigh-ins never leave your phone
- No streaks
- No cap on logging, ever
What it costs
Free to use. Plus if you want the better reader.
Two models read plates for Marble, both made by Anthropic. Free uses Claude Haiku, which is fast and fine for most meals. Plus uses Claude Sonnet, which is better at judging how much is on the plate. Your first two weeks are on Plus, with no card.
Free
$0, for good
- Three plates a day read by Claude Haiku — a photo, or a description
- Typing a meal in, barcodes and repeats: unlimited
- Weigh-ins, your trend, and every correction
Plus
$4.99 a month
- Every plate read by Claude Sonnet, no daily limit
- The coach — real answers about your week, from your own record
- Corrections — tell it what it got wrong and the numbers recompute
Questions
The ones worth answering honestly.
How accurate is a photo, really?
It's an estimate. But reading your meals a little low every time just means the corrected target settles a little lower to match — and your results still land where you wanted them. Consistency matters more than accuracy here.
Do I have to weigh myself every day?
It's the thing that makes the rest work, and it takes ten seconds. Daily is also less stressful than weekly: when every reading is one dot in a line, no single morning is a verdict.
What does it cost?
Your first two weeks are on Plus, with no card: every plate read by Claude Sonnet, and the coach. After that Marble stays free — three plates a day read by Claude Haiku, and typing a meal in, scanning a barcode or logging a past meal again are always unlimited. Plus is $4.99 a month and keeps Sonnet on every plate, the coach, and corrections. Sonnet is the better reader of the two, mostly at judging portions; Haiku is fast and fine for most meals.
Where does my data go?
Your weigh-ins never leave your phone; the trend and every correction are computed on the device. Meal photos are sent to be analysed, and that's the only thing that goes out. Detail on the privacy page.
Is this a good idea if I've struggled with food?
Talk to a doctor or a dietitian first. Marble hides single readings, refuses to celebrate streaks, and tells you when a scary morning is meaningless — but it is still an app that counts, and counting isn't right for everyone.
Stop trusting the number.
Start measuring it.
Free, no account, and it will tell you when it's wrong.