Smartpaper Letters Developer Interview: 10,000 Sandpaper Letters on a Tablet

StudyX Smartpaper Letters is a handwriting app that turns the Montessori sandpaper letters into a digital tool. Version 1.0.0 was released on the App Store in July 2025. You type any string of characters, trace the animated model one stroke at a time, and get a score when you finish. It runs on iPad and iPhone.

Version 1.1.0 in July 2025 added the Montessori style for letters and numbers (vowels in blue, consonants in red, numbers in green) and simplified Chinese. Version 1.1.1 in May 2026 brought traditional Chinese and Korean Hanja character forms and handwritten input for search, and 1.1.2 in October put the interface into 14 languages. The app holds more than 10,000 characters across hiragana, katakana, kanji, the alphabet and numbers, and it is a one-time purchase. I asked hiroki, who made it, about how it started and how they think about it now. The answers are kept as close to the original Japanese as translation allows.

It started with the sandpaper letters

Q. What first made you want to build Smartpaper Letters? Did you start from the sandpaper letters as a specific material, or did you first want to make an app for beautiful handwriting?

I started from the Montessori sandpaper letters as a specific material. The idea was that in digital form, the number of characters could grow enormously. I built an experimental version and tried it. The rough feel of sand cannot be reproduced, but on an iPad with a paper-like screen protector, it worked quite well. So I finished it and released it.

Q. Version 1.0.0 came out in July 2025. Kakikata, your hiragana and katakana app, also has tracing. What did you build new for Smartpaper Letters, and what did you carry over?

Basically I built everything from scratch. I implemented tracing in Kakikata, but Smartpaper Letters does it with a different mechanism. I used Kakikata as a reference, but technically it is a separate thing.

Q. The app is スマもじ (Sumamoji) in Japanese, Smartpaper Letters in English and 砂字版 in Chinese. Why are the names so different?

They are all plays on the name of the Montessori material, the sandpaper letters. I chose names that make someone who knows Montessori education think, “I see.”

Handwriting shows the person

Q. Do you like writing by hand yourself? Have you ever wanted to write beautifully?

The longing for “beautiful handwriting” may be particular to Japan and China, where there is a culture of calligraphy, but I have a strong interest in handwriting too. My own handwriting is not neat, but when I see someone with beautiful handwriting, I think, “That’s nice.” I think neat handwriting makes both the writer and the people around them happier than messy handwriting. I want my children to write neatly. Handwriting seems to reflect a person’s character and personality, which I find interesting.

Q. How did you become interested in Montessori education, and why the sandpaper letters in particular?

My children are being raised with Montessori education. They go to a Montessori school, and we have studied Montessori education ourselves and practise it in our parenting every day. We own sandpaper letters and use them at home, but for the characters used in Japanese, there are many letter boards that have never been made.

Smartpaper Letters has close to 10,000 characters. Making those in real woodwork would cost an enormous amount, and there would be nowhere to keep them. Making them portable, usable anytime and anywhere, was reason enough on its own to make it a tablet app.

The sandbox makes up for the touch

Q. The key thing about real sandpaper letters is the rough texture, and a screen is smooth. What is lost by going digital, and what is gained?

As I said earlier, the feel of touch is lost. But I think that can be made up for by not ending with the tablet: writing letters in a sandbox with your own finger or a wooden stick, alongside the app.

What matters is giving children, when they reach the sensitive period for writing, a chance to become absorbed in an experience that uses their body and all five senses. Smartpaper Letters is not perfect for that, but I think it is useful as one tool.

Q. Each time you finish a stroke, the animation for the next one starts. You could have shown the whole stroke order first. Why one stroke at a time?

I designed it to be easy for children to actually use.

Q. There is no list of characters by grade or a kana chart. You type any string into the search bar, and the placeholder says “any letters you like.” Why free input?

Because children want to write the letters they like.

Q. The Montessori style colours vowels blue, consonants red and numbers green, but hiragana and kanji get no colour. Why?

Because hiragana and kanji are different from the alphabet.

Q. For Korean, the app supports only Hanja, not Hangul. Why offer a Korean interface and store page anyway?

I would like to support Hangul in the future, but for now I thought Hanja alone could be useful, so I released it.

Q. If you choose pinyin or zhuyin and write by hand, you practise the character forms of that region. The same character looks slightly different in Japan, mainland China, Taiwan and Korea. Why take such care with those differences?

Because the differences between languages are completely different things, even when the shape or meaning looks similar. They look alike but are not the same.

The score is for checking your own accuracy

Q. The store description covers everyone from small children learning letters to adults practising pen writing. Who do you most want to use it?

Children aged 3 to 6 who are in the sensitive period for letters.

Q. The description says learners can practise alone without a parent or teacher beside them. Montessori values materials that let children notice their own mistakes. Do you worry that a score makes them depend on outside judgement?

The tracing score is not outside judgement. It is a measure for checking your own accuracy. When you play at raising your score, you naturally end up practising again and again. Personally, I like that kind of quiet game design. People who do not need the score can turn it off.

Writing by hand is a path

Q. In an age of keyboards and voice input, how do you explain the point of practising handwriting?

It is a path, something like the value of mastering a thing. Just as the question “Is there any point to calligraphy?” has no point, I think that question has no point either. Whether you care about writing well is a personal matter.

From the point of view of brain science, though, handwriting is an important habit that activates the brain. I think it is fair to say that children no longer writing by hand is clearly bad for their brain development.

Q. Real sandpaper letters have about 26 letters, and the app has more than 10,000 characters. Has the larger number made it less like the sandpaper letters?

The number of characters is far larger, yet the price of the material has become very reasonable. The real material is handmade woodwork, so it costs something like 50,000 yen. Many more people around the world can use it now, and you could see it instead as an evolved version of the sandpaper letters. I want to keep adding characters.

Q. Were there features that did not work, or that you added and took out?

I don’t remember. Basically I keep it simple.

Used by serious Montessori families

Q. In Japan the app has 9 ratings with an average of 4.8. Are there reactions or uses that stayed with you?

It is used quietly and rated well quietly. It has good points you only notice once you use it, but it is paid. So it is used by the serious Montessori crowd.

Q. It is also downloaded outside Japan. How do you picture people abroad using it?

It supports Chinese and English letters too, so it is used all over the world. It is used in a Montessori way.

Priced against the real material

Q. Smartpaper Letters is a one-time purchase of 1,500 yen in Japan, with no in-app purchases or ads. Its sister app Kanjin starts free and unlocks everything through a purchase. Why make Smartpaper Letters paid from the start, and how did you set the price?

I thought people would compare it with the real Montessori sandpaper letters and buy it, so I made it a paid app. The price is based on a single worldwide price of 9.99 dollars.

Because you can use it as soon as you buy it, I think a paid app is best where possible. But the App Store is now flooded with free apps, and paid apps have become relatively weak in store search. Apple does not look after paid apps, so they are hard to get found. That is why my recent apps are free with in-app purchases.

Q. Among your apps for writing Japanese, there are Kakikata for hiragana and katakana, the Aiueo chart app, Kanjin for kanji, and Smartpaper Letters. How do you divide their roles?

I think each meets a different need.

More characters to come

Q. What would you like to add next?

I want to support more languages, so I want to keep increasing the number of characters. I don’t know yet whether that will be in this app or in a sequel, but I want to take it on.

Q. If you rebuilt Smartpaper Letters from scratch today, what would you change?

Nothing.

Letters learned young last a lifetime

Q. Years from now, if someone learned their letters with Smartpaper Letters, what do you hope stays with them?

Letters learned in early childhood are literacy you can use for life, for writing and for reading. I hope they write lots of characters and keep learning more.

Q. Is there anything else you want to say about Smartpaper Letters?

If anything is hard to use or you would like something fixed, please feel free to get in touch. Feedback is always welcome.

About Smartpaper Letters

StudyX Smartpaper Letters is a handwriting app with more than 10,000 characters: hiragana, katakana, Japanese kanji, simplified and traditional Chinese, Korean Hanja, the alphabet in print and cursive, and numbers. Type any string, trace the stroke order animation one stroke at a time, and get a score when you finish. Words you want to practise go in a word list, and your scores are kept in a history. It is a one-time purchase with no in-app purchases or ads.

How to start is in Getting Started with StudyX Smartpaper Letters, and the material it is based on is explained in Montessori Sandpaper Letters. For details about the app, see the Smartpaper Letters page.