Make it fit. Have enough yarn. Every time.
Cast On turns Claude into the friend at knit night who's great at math. Turn your swatch into real numbers, resize patterns, space increases evenly, swap yarns safely, work out how many skeins to buy, and design simple hats, socks and blankets that fit.
Get Cast On Pattern Helper for $15 Check my gauge
- One-time $15
- Instant email delivery
- 14-day refund
- Works on any Claude plan, even free
Gauge check: Harbour Pullover, size 40
Pattern 20 sts / 4 in · your swatch 18 sts / 4 in, washed and blocked
Comes out 44.4 in4.4 in too big2 ways to fix
- Math200 sts ÷ 4.5 sts per in = 44.4 inThe pattern expects 5 sts per in for 40 inToo big
- Fix 1Go down to a 4 mm needle and re-swatchBest if you like the fabric's feel at a tighter gaugeTry first
- Fix 2Knit the 36 size at your gauge180 sts ÷ 4.5 = 40 in · lengths in inches stay the sameOr this
- YarnBuy 6 skeins of 220 yd, same dye lot1,150 yd needed + 1 spareShop
All the math knitters and crocheters dread
One skill for gauge, sizing, yarn and pattern help. Knit and crochet, US or UK terms, inches or cm.
Gauge math
Your swatch turned into stitches per inch and the size your project will really come out.
Resizing
Stitch counts recalculated for any size, rounded to the pattern's stitch multiple.
Even increases and decreases
"Increase 10 evenly across 64" turned into a line you can follow.
Yarn substitution
Weight, yardage, fibre and drape compared, and how many skeins to buy.
Simple pattern design
Hats, scarves, cowls, socks, blankets and amigurumi with real measurements and ease.
Pattern help and fixes
Abbreviations, chart reading, US versus UK crochet terms, and fixes for common mistakes.
Ask it like you'd ask the knitter who does everyone's math
It shows the working, so you can check before you cast on.
Work it like this (64 sts → 74 sts)
64 ÷ 10 = 6 with 4 left over, so you need 4 sections of 7 stitches and 6 sections of 6 stitches, with an increase after each.
K3, M1, *K7, M1* 4 times, *K6, M1* 5 times, K3.
That's 3 + 28 + 30 + 3 = 64 stitches worked, with 10 increases spread evenly, and half a section at each edge so it's balanced when you seam.
Working in the round? Skip the half sections: *K7, M1* 4 times, *K6, M1* 6 times.
Math you can check
Cast On never just gives you a number. It shows how it got there.
- Working shownEvery count, measurement and yardage comes with the calculation.
- Pattern multiples respectedCounts rounded to fit the rib or stitch repeat, and it tells you which way it rounded.
- Your termsUS or UK crochet terms, knit or crochet, inches or centimeters.
- Respects designersHelps you resize for your own use without copying a pattern's text or charts.
Up and running in two minutes
No app to learn and nothing to install on your computer. It lives inside Claude.
Buy once
Pay $15 by card, Apple Pay or Google Pay. Your download link arrives by email in about a minute.
Add it to Claude
Upload the ZIP in Claude under Customize, then Skills. It takes about 30 seconds. No setup, no accounts.
Just ask
"My gauge is 18 sts and the pattern says 20. Now what?" "Design a slouchy hat in worsted." "How many skeins of this DK?"
Start with the free Gauge Calculator
A small skill that turns your swatch into gauge, shows how big your project will really be, and works out how many skeins to buy.
- Your real finished size
- Needle change or new cast-on count
- Skeins to buy, with a spare
Get Cast On Pattern Helper
Pay once, use it on every project. Includes the free Gauge Calculator too.
How to add it
- Claude on the web or desktop: don't unzip it. Open Customize, then Skills, click +, choose Upload a skill and pick the ZIP. It works on any Claude plan, including the free one: just turn on code execution in Settings, Capabilities.
- Claude Code:
unzip cast-on-pattern-helper.zip -d ~/.claude/skills/ - Start a new chat and try: "My swatch is 18 stitches over 4 inches and my pattern wants 20. Help me get this sweater to fit."
Cast On Pattern Helper
Gauge, sizing, yarn and pattern help in one.
$15 one time
- Gauge math and finished sizes
- Pattern resizing
- Evenly spaced increases and decreases
- Yarn substitution and skein counts
- Simple pattern design
- Abbreviations, charts and fixes
- Project tracking
- Updates for a year
Secure checkout by Stripe. Taxes calculated at checkout. 14-day refund.
Prefer to buy on Etsy? Get it on Etsy
New to Claude?
Claude is an AI assistant made by Anthropic, like ChatGPT. Cast On is a skill: a set of expert instructions you add to your own Claude account, so Claude answers like a knitter who's great at math who knows the craft.
- Make a Claude account at claude.ai. Skills work on every plan, including the free one; paid plans give more usage.
- Turn on code execution in Settings, Capabilities (skills need it).
- Try the free Gauge Calculator skill first. If you like it, the full skill is one purchase.
Not ready for Claude? The free gauge calculator on this site works in any browser, no account needed.
Questions
Knit and crochet?
Both. It handles knitting and crochet math, and uses US or UK crochet terms as you prefer (a US single crochet is a UK double crochet).
Can it read my pattern?
Share the numbers you're working with and it will recalculate or resize them for your own use. It won't reproduce a designer's paid pattern text or charts.
Can it design a whole sweater?
It's best at simple pieces (hats, scarves, cowls, socks, blankets, amigurumi basics) and at resizing existing patterns. Complex garment design is better done with a full pattern.
Metric?
Yes. Tell it you work in centimeters and grams and it does everything in metric.
What do I need to use it?
A Claude account on any plan, including the free one, with code execution turned on (Settings, Capabilities). Free accounts have lower usage limits, so long planning sessions go further on a paid plan. It works in Claude on the web, the desktop app and Claude Code.
What if it doesn't work for me?
Email hello@whatiflabs.ai within 14 days of buying and we'll refund you in full. No forms, no questions.