# Learning Transformer — Attention, one step at a time

> Attention, one step at a time (iPhone/iPad app by Sungjun Kim.)

- Source: https://appshunter.io/ios/app/learning-transformer/id6802260008 (this page in markdown: same URL + `.md`)
- Developer: [Sungjun Kim](https://appshunter.io/developer/1602461985)
- Category: Education, Reference
- Price: Free with in-app purchases
- Age rating: 4+
- Requires: iOS 17.0 · 1 MB
- Languages: American English
- Released: 2026-08-21
- Data updated: 2026-10-08
- User reviews in markdown: https://appshunter.io/ios/app/learning-transformer/id6802260008/reviews.md

## What is Learning Transformer?

A Transformer, built by hand and shown one step at a time.

Twenty-three screens follow "Attention Is All You Need" (Vaswani et al., 2017) in the paper's own order: a word becoming numbers, the three vectors, the scores, the softmax, four heads merged into one, the mask, the second attention, and the loop that writes one word at a time.

What this is not: a trained model. Every weight here was set by hand, so that each one can be read in a single line. Nine numbers stand for a word instead of 512. One encoder layer and one decoder layer instead of six of each. Four heads, four words of vocabulary, one short sentence.

What it is: the paper's arithmetic at a size you can check by hand. Every number on every screen is computed while you look at it — no videos, no quizzes, no account, no network.

Steps 1 to 10 are free. Steps 11 to 23 are one purchase, made once and kept.

## Pricing and in-app purchases

Base price: Free.

**One-time purchases**

| Purchase | Price | Type |
| --- | --- | --- |
| the decoder | $3.99 | one-time |



## Version history (last 1 release)

### 1.0 — 2026-08-21

No release notes.

## More apps by Sungjun Kim

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- [game theories 1](https://appshunter.io/ios/app/game-theories-1/id6443715938)
- [game theories 2](https://appshunter.io/ios/app/game-theories-2/id6443716105)
- [relativistic velocity addition](https://appshunter.io/ios/app/relativistic-velocity-addition/id6443873136)
- [relativistic space travel](https://appshunter.io/ios/app/relativistic-space-travel/id6443974500)
- [Learning Hangul](https://appshunter.io/ios/app/learning-hangul/id6449379992)

All apps by Sungjun Kim: https://appshunter.io/developer/1602461985

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-10-08.*