For skinny guys who want to put on size

Eating big, made easy.

239g protein · 3,311 kcal · your numbers, handled

Download on the App Store Get it on Google Play
Watch how it works · 30 seconds
Browse all 81 meals →
★★★★★ 5.0 App Store · No ads · No account · No paywall
Works with ChatGPTClaudeGeminiDeepSeek + any AI
Built for hardgainers

If you're a skinny guy, you know the drill.

Appetite gives out halfway through dinner.
The scale won't move no matter what you lift.
Every meal is the same chicken and rice.
Every bulking guide assumes you love cooking.
"Just eat more, bro," as if it's that easy.

JSON.fit is built for exactly this. The meals, the macros and the prep are handled, so the only hard part left is showing up.

The Meal Library

81 real meals, every step written.

Browse all meals →
Slow-Cooked BBQ Pulled Pork
Australian · Pork
Slow-Cooked BBQ Pulled Pork
48g P28g C32g F610 kcal
 Red Wine-Braised Lamb Shanks
Australian · Lamb
Red Wine–Braised Lamb Shanks
54g P14g C58g F825 kcal
 King Kong Chocolate protein smoothie
Smoothie · Dairy
King Kong Chocolate
85g P93g C79g F1418 kcal

Swipe to see more →

Browse all meals →
FREE
JSON.fit
The Skinny Guy's Bulking Cookbook
81 calorie-dense meals
Free Cookbook + Updates

All 81 meals, free.

The printable cookbook, macros and ingredients included, plus new meals as they land and my bulk to 90kg in the open. First access and a launch discount when the print edition drops.

✓ Check your inbox, your cookbook's on the way.

No ads, no spam. Unsubscribe anytime.

How your plan gets built

Any AI in. Real plan out.

Meal plans and full training programs, up to a year long, from the same three steps.

01 · You answer
A few quick questions
GoalWeight gain
Target90kg
Meals6 per day
Training4 days/week
Copy prompt

Your goal, stats and favourite meals become a research-packed prompt. One tap to copy.

02 · Any AI writes
meal-plan.json · from ChatGPT
{
"plan": "7-Day Lean Bulk",
"kcal": 3311,
"protein_g": 239,
"meals": [{
"name": "Massaman Beef Curry",
"kcal": 890 }]
}
ChatGPTClaudeGemini+ any AI

Paste it in. The AI writes your week on real research and returns it as JSON.

✓ 0.81S
03 · JSON.fit imports
7-Day Lean Bulk✓ IMPORTED
Protein Pancakes
6:00 AM · 760 kcal
Massaman Beef Curry
12:30 PM · 890 kcal
One grocery listPrep in one sessionExact macros

Import the file. Macros, groceries and the week's prep, handled.

Built on peer-reviewed
training and nutrition science

See It Working

Real AI output.
Take it for a spin.

An actual user's plan, generated and imported with Claude. Tap the phone to switch between the day's meals and the workout log.

Itemised shopping list with prices
One priced shopping list. A week of food in a single trip.
9:41
‹+
JUN 9
Tuesday
117 / 239g protein · 1,580 / 3,311 kcal
2 of 5 eaten
Timeline
6:00 AM · BREAKFAST
›
Protein Pancakes
760 kcal · P52 C74 F27
9:00 AM · BRUNCH
›
Steak & Eggs
820 kcal · P65 C37 F44
12:30 PM · LUNCH
›
Slow-Cooked Massaman Beef Curry
890 kcal · P52 C42 F58
4:00 PM · SNACK
›
King Kong Chocolate
1418 kcal · P85 C93 F79
7:30 PM · DINNER
›
Slow-Cooked BBQ Pulled Pork
610 kcal · P48 C28 F32
exercise demo
‹
⋯
Barbell Back Squat ▾
Quads · Glutes
Week 13 × 10, 10, 8
SETKGREPS✓
1
0
10
2
0
10
3
0
8
+ Add set
UP NEXT
Barbell Back SquatCURRENT
3 × 10, 10, 8 · 0/3 done
Romanian Deadlift
3 × 10 · 0/3 done
Leg Press
3 × 12 · 0/3 done
0:00
Start Workout
Tap to switch
Step by step meal prep session
Step-by-step prep that clears the week's cooking in one go.

Swipe to see more →

The Lab
Not just claims. I'm bulking in public.

Real body scans, tracked monthly and published, from 77.3 kg to 90 kg. Same skinny guy this app is built for.

See every number
Ryan, founder of JSON.fit RN
Why I built this

I built JSON.fit because I'm the guy it's for.

I'm a skinny-by-default lifter who got sick of force-feeding myself and fitness apps that assume cooking is my hobby. So I built the thing I actually needed: big meals with the steps done for me, macros handled, prep that fits around a full-time job.

I'm bulking to 90kg on it in the open, so I use this app every day. When something's clunky or missing, I feel it first and fix it, which is why it keeps getting better. No team, no investors, just me, building the tool I wish I'd had.

Ryan, solo founder

Read the blog The Lab
Free Training Programs

Eating big adds the weight.
Training makes it muscle.

Build a custom program with the same three steps: your split, your equipment, up to a year long. Or import one of these, periodised and ready today.

Upper / Lower

Beginner Foundation

4 training days · 3 rest
52 weeksBeginner
Preview & import PPL + Upper/Lower

Intermediate Hybrid

5 training days · 2 rest
54 weeksIntermediate
Preview & import Push / Pull / Legs ×2

Advanced High-Volume

6 training days · 1 rest
52 weeksAdvanced
Preview & import
Compare

Premium personalisation.
Zero cost.

The kind of programming and nutrition that used to cost a fortune, now completely free.

JSON.fit
Dietitian / PT
Other Apps
Typical cost
Free
$150–300 USD/session
$20–60 USD/mo
Expert-level personalisation
✓
✓
Basic
Instant access
✓
Weeks wait
✓
Unlimited plan changes
✓
✗
✗
Grocery lists
✓
✗
✗
Meal prep guidance
✓
✗
✗
No ongoing fees
✓
✗
✗
AI provider choice
Yours
N/A
Locked in
App Store Reviews

What people are saying.

5.0 ★★★★★ Rated 5.0 · App Store
★★★★★
Awesome app, fitness plans

Created me a 12 week fitness plan for all my personal priorities. Was even able to add additional preferences via AI.

Rory@TVX · 23 May · Australia
★★★★★
Replaced my $30/month PT app

Was paying for an AI trainer that was just GPT under the hood anyway. This app lets me use ChatGPT myself to build my program and just handles the tracking. Workouts are completely free too which I wasn't expecting.

ReeceAdam · 31 Mar · Australia
★★★★★
Finally an AI fitness app that doesn't charge you for AI

Already pay for ChatGPT Plus so I was sick of other apps charging me again for the same thing. JSON.fit lets me use my own AI and just handles the tracking. Workout imports are completely free.

Zac ishiyama · 4 Apr · App Store
No subscription

Everything free. No catch.

$0to use
✓ Full bulking meal library, step-by-step
✓ AI meal plans built around your macros
✓ Free year-long training programs
✓ Smart grocery lists & pantry intelligence
✓ Works with ChatGPT, Claude, Gemini & more
✓ No ads, no accounts, nothing sold. Ever.
Download on the App Store Get it on Google Play

🔒 Your workouts & nutrition stay on your device.

📱 iPhone & Android

FAQ

Common questions.

Three steps:
1. Answer a few quick questions.
2. Paste the prompt JSON.fit makes into any AI like ChatGPT, Claude or Gemini.
3. Import the meal plan it builds and start tracking.

The same flow builds your training program too.
Most AI chatbots have a free tier that works perfectly. ChatGPT, Gemini and others all offer free access. If you're already paying for a premium AI subscription, even better. Either way, JSON.fit itself has no AI costs to pass on to you.
It's completely free. Workouts and nutrition are all free: meal plans, macro tracking, grocery lists, meal prep and pantry intelligence. No subscription, no paywall, no in-app purchases.
That's exactly who it's built for. You answer a few questions once, import the plan, then cook in batches off a single grocery list. Most of the week's food gets handled in one prep session, so eating in a surplus fits around work instead of taking it over.
Building or importing a plan takes a few minutes. After that it's one shop and one prep session for most of your meals, then quick logging as you go. The whole point is to hit your macros without bulking turning into a second job.
There isn't one. Most fitness apps charge $10–20/month because they run AI on their own servers. JSON.fit uses the AI you already have, so there are no server costs to pass on. There are no ads, and nothing is sold. Your workouts, meals and health data stay on your device, and like most apps and websites JSON.fit collects anonymous, non-identifying usage analytics to help improve it. The app is simply free.
Any AI that can generate structured text, like ChatGPT, Claude, Gemini and DeepSeek. You're not locked into one provider. Use whatever you prefer.
Yes. Your workouts, meals and health data stay on your device and are never uploaded. JSON.fit has no accounts and doesn't collect personal information. Like most apps and websites, it uses anonymous, non-identifying usage analytics (such as Google Analytics) to see how it's used and improve it. Full details are in the Privacy Policy.