Independent iOS product · 2021–present

Flashcard Dictionary

Every lookup becomes a flashcard: look a word up, tap the star, and it joins your reviews. I have designed, built and run this subscription vocabulary app for iOS on my own.

Try the interactive prototype
Word page for run, with a star to save it and its meanings on cards
Home with a demo deck: 6 words to review, a blue Review now button, a search field and recent lookups
Review card for ephemeral: the prompt Know what it means? above three buttons, Don’t know, Not sure and Know it
The word page, Home and a review card in 5.4.
Role
Product designer & developerProduct design, Swift development, StoreKit subscription integration and long-term operations, all solo
Platform
iOS · View on the App Store 
Timeline
2021–presentLaunched in 2021; updated to 5.4 in October 2026 and to 5.5 in November 2026
Design system
Open in Figma Tokens, components, rules and key screens, taken from the 5.4 code

Project outcomes

50,000+App Store downloads worldwide
0 → 1Interviews → design → Swift → App Store → operations, one person
01

The problem

You looked the word up. Then what?

I surveyed and interviewed English learners at different levels. They shared one gap: after a lookup, there is no next step.

A dictionary ends at the definition. Vocabulary apps have a review rhythm, but the word list is someone else’s and rarely matches the words you meet.

So the goal was to put remembering inside the act of looking up.

  1. Words don’t stickLearners forget words they studied days ago, even after repeated exposure.
  2. Traditional flashcards feel monotonousRepetitive, non-adaptive drilling makes people stop opening the app.
  3. People want to see progressMost wanted to measure their progress instead of relying on a feeling.
  4. Short sessions winLearners prefer short study sessions that fit into their day, without setting aside a block of time.
More detail: the two personas
  1. Persona 01

    Yang Kaihan · 22 · college student preparing for the GRE

    Pain pointsStruggles to remember new words despite frequent exposure; finds existing apps either too simplistic or too cluttered with distractions; needs a structured way to track progress.

    GoalsExpand GRE vocabulary efficiently; retain words through a structured, adaptive method; use a distraction-free mobile tool that fits a daily study routine.

  2. Persona 02

    Alejandro Torres · 30 · product marketing manager in Seattle

    Pain pointsAs a non-native speaker, struggles with nuanced vocabulary in business communication; existing apps feel too academic for his career; has no hours to spend studying.

    GoalsImprove the vocabulary of his professional communication; learn words that apply directly to marketing and business contexts; a structured tool that fits a busy schedule.

Each existing app was missing a piece

Anki, Quizlet, Duolingo, Merriam-Webster and Baicizhan each covered part of that path, but none put lookup, card-making, review and progress in one place.

02

The solution

Interactive prototype

An interactive re-creation of version 5.4, from lookup to review.

This interactive prototype needs JavaScript. Screenshots of the real app appear further down.

No second app to open, no card to make

You look up, save and review; the app makes the card and picks when it returns.

Look a word up
Tap the star
Makes the word a card, due for review at once
Review up to 12 cards a round, making a call on each before the answer shows
Sets the next review for when your recall chance falls to 90%
When it’s due, the word comes back to review
The loop as the app runs it since 5.4.

Words come back before you forget them

Since 5.4, FSRS-6 schedules reviews: the open-source scheduler built into Anki, fitted on millions of real reviews. Each grade updates how stable a word is in memory.

The familiarity bar shows that stability as a percentage and a color, so every saved word shows how well you know it.

More detail: the scheduler
90%Recall chance at which a word comes back
÷ 28 daysFamiliarity: stability in days ÷ 28, up to 100%
21 daysStability that counts as Memorized; Learning starts at 7
1 yearLongest gap between two reviews

The scheduler is a port of py-fsrs 6.3.2 with its default parameters, and it reproduces py-fsrs’s own test values. Due words come lowest recall chance first, and a first Know it then Got it brings a word back in two days.

The paywall waits until you want one more word

I put the paywall at the moment someone wants to keep one more word, not at launch. People go through looking up, saving and reviewing before they hear about subscribing.

10Words saved for free
11thIn 5.4, starring it opens the monthly and yearly plans
More detail: purchases in 5.4

In 5.4, Premium is checked on the phone with StoreKit 2, with no third-party SDK in between.

The paywall shows App Store prices, restore, a renewal note and the Terms and Privacy links, and the free limit is shared by the English and Korean decks.

03

Iterations

After launch: small releases, then 5.4

Most releases came from user feedback, and one experiment was tried and taken back out.

  1. 20211.0 ships

    Lookup, saving, flashcards and the familiarity score.

  2. Late 2021Subscriptions

    A free limit, monthly and yearly plans, restore.

  3. 2022Saved Words

    Sorting, swipe to delete, search suggestions.

  4. 20235.0

    Simpler Home and cards; movie quotes picked by AI, later switched off.

  5. 2025Tab bar

    Home and Saved Words become tabs.

Version 5.4, in October 2026, redesigned Home, the review and the colors.

Home gave no reason to come back, so it now leads with what’s due

The 5.3.1 Home was a search field on red. Unless you had a word to look up, nothing there gave you a reason to open the app, and reviewing sat a tab away.

So 5.4 moves review onto Home: a card says how many words are due, about how long they take, and how many are memorized, learning or still to learn.

The trade-off: search, the app’s first job, moved below the card. Tapping the field folds the card away, so a lookup still starts with one tap.

Before · 5.3.1

5.3.1 Home: a red screen with the Flashcard Dictionary logo, a Powered by Oxford Languages badge, a white search field and a green Search button

Search on red, and nothing to come back for.

  • Home tab
    • Search
      • Word page
    • Menu
  • Favorites tab
    • Saved Words
      • Review: pick an order
        • Every saved word, no end screen

After · 5.4

5.4 Home with a demo deck on a cream page: Memo, a cartoon elephant boxer, says “6 words in the ring. Ready?” above a white card reading 6 words to review, about 2 min, with 12 Memorized, 7 Learning and 5 To learn, +4 memorized this week and a blue Review now button; a search field and recent lookups below

What’s due comes first; search and recent lookups sit below.

  • Home tab
    • Review card
      • Due words, 12 at most
        • Review done: when to come back
    • Search
      • Word page
    • Recent lookups
    • Menu
  • Favorites tab
    • Saved Words
      • Review: pick an order
        • Every saved word
          • Review done
Structure drawn for this page from the app’s source, main paths only. 5.4 uses a demo deck.
More detail: the first save

A newly saved word is due at once, so Review now appears after the first star. Testing the first run showed that a new learner would otherwise see All caught up before reviewing anything.

Ask for the call before showing the answer

Through 5.3.1, a review turned the card over and then asked whether you remembered it. With the meaning already on screen, Remember feels true even when it isn’t, so answers ran high. Since 5.4, you make a call before the card turns over, then check it against the answer.

Review card 1 of 6 from a demo deck, front: ephemeral on a blue card with Memo reading on its top edge, the prompt “Know what it means?” and three buttons, red Don’t know, yellow Not sure and green Know it, under a progress bar reading 1 / 6
1 · Front: make the call before you see the meaning.
The same demo-deck card turned over after Know it: a white card with ephemeral and its Adjective meaning and two examples, a white Full Definition button, then red Missed it and green Got it buttons
2 · Back: did the call hold up?
Quick check card with Memo thinking on its top edge: a green Memorized check pill, the prompt “Which word means this?”, a meaning with the word replaced by a blank, and four word options taken from the demo deck
3 · Quick check: a multiple-choice card, with wrong options from your own words.

5.4, demo deck.

More detail: grades and quick checks

Each card gets one grade, saved after the back: Know it then Got it is Good, Not sure then Got it is Hard, and everything else is Again. A right pick in a check is Good and a wrong one Again.

A check needs 4 saved words and 2 wrong options with the same part of speech, or the card stays a normal call. Checks skip a word’s first review, which is for learning it, and Korean cards.

About one card in six becomes a quick check, since the rest already ask for a call.

Review screen of an earlier build: the flipped renegade card shows two definitions above a Full Definition button and the Don’t remember, Vague and Remember buttons
Before 5.4: flip first, then rate with the answer in view (an earlier build).

Color means one thing: how well you know the word

In 5.4, the app is redrawn as flat stickers on cream. Red, yellow and green mean familiarity and nothing else, and primary buttons are sky blue; mustard came first but sat too close to the familiarity yellow.

A hard shadow marks what you can press, so cards and bars lie flat. The three familiarity colors also differ in lightness and always come with a label, percentage or icon. These rules, the tokens and every component are written down in the app’s Figma design system .

Saved Words with a demo deck: the title “You are learning 24 words”, then white rows each with a word, a percentage and a red, yellow or green bar, empty at 0%; a Sort by sticker at the top right and a blue Review button floating at the bottom
Saved Words: each bar takes its band’s color next to the percentage. 5.4, demo deck.

Explain words in the learner’s language

The one App Store listing reaches China as well as the U.S., but the interface was English only. In 5.4, the app adds Simplified Chinese, picked by the App Store region rather than the phone’s language and switchable in Settings.

In Chinese, an English word opens with short Chinese meanings from a dictionary bundled in the app, so they work offline for every saved word, at the cost of about 20 MB.

Chinese interface · 5.4

Word page for run in the Chinese interface: a 中文释义 card listing Chinese meanings for noun, verb and adjective, then the English definitions under Chinese part-of-speech headings
The word run in Chinese: short meanings first, then the English definitions.
More detail: Korean, sources and offline

In 5.4, English speakers can also learn Korean: look up in English or Korean, pick the meaning you mean, and see Revised Romanization. Korean is a separate deck whose saved list hides meanings, so it doesn’t give away review answers.

Since 5.4.2, the China store also lists the app with its own Chinese name and screenshots: 闪卡词典-高效记忆单词.

Korean meaning picker titled “Which bank?”: two rows, institution → 은행 eun-haeng, with an example sentence and its English translation, and edge of river or lake → 둑 duk
Korean: pick which bank you mean.

English definitions come from Simple English Wiktionary first, because its entries are written for learners, then from the full English Wiktionary. They appear as one card per part of speech, with numbered meanings and each example under its meaning.

Flashcard Dictionary 5.4: an iOS appSwift · UIKit · Core Data · StoreKit 2
On the deviceSuggestion word list · saved words and definitions · FSRS scheduler · ECDICT Chinese meanings
Online sourcesSimple English Wiktionary, then English Wiktionary · Wikimedia Commons recordings · KRDict for Korean words Wiktionary lacks

Since 5.5, the rest of the dictionary comes with the app too (about 140,000 English words and the Korean dictionary), because Wiktionary doesn’t always load in mainland China, so most lookups work offline.

Saved words open offline, and a failed lookup says so and offers Try again. Since 5.5, a misspelled English word gets “Did you mean…?” with the closest spellings.

04

AI recall check

AI checks the answer, and the learner decides

In 5.4 the learner still judges their own answer. AI review, new in 5.5, asks for the answer itself.

  1. 5.4 · You judge yourselfBefore the card turns over, you tap Don’t know, Not sure or Know it, then check your call against the answer.
  2. 5.5 · AI judges your answerBefore the card turns over, you say or type what an English word means, and AI checks it against the word’s saved meanings.

You can accept the AI’s call, change it, try again or tap I don’t know. On my iPhone, an early build’s reason gave the meaning away, which made Try again pointless; now the reason only says what was right or wrong.

Self review stays the default: answering and waiting for a verdict is slower than a tap and needs a connection, so AI review is a switch on Home’s review card and in Settings.

AI review card 1 of 6 from a demo deck: under You said, the answer “short-lived, only lasts a moment” and a Try again link; a green panel reading AI’s call, You know it, with a check mark; the reason “You described it as short-lived and lasting only a moment, which matches its meaning.”; Change and Accept buttons below the card
The AI’s call and its reason. 5.5 in the iOS Simulator with a demo deck; the verdict was set for the screenshot.
More detail: how a call is made

The AI’s three calls, You know it, Partly there and Not yet, stand for Know it then Got it, Not sure then Got it, and Don’t know, so FSRS grades them the same way. Change shows all three on the same card, with the AI’s marked.

If the AI is less than 60% sure, or doesn’t answer in time, the card shows no verdict and you make the call. Answers can be in English, or in Chinese when the app is in Chinese. Korean cards keep the self-review calls.

An early build switched back to the self-rating buttons partway through a card whenever the AI couldn’t judge. On the phone that felt broken, so Self and AI became two separate modes.

Calls made by accepting the AI stay out of How your calls held up, since they aren’t the learner’s own judgement.

Before any app code, the judging prompt was run on 12 hand-written cases, among them a misheard word, a Chinese answer, a second sense of the word and an answer that told the judge what to say. All 12 came back as expected.

05

Results

Still updated, more than four years after launch

Flashcard Dictionary has passed 50,000 App Store downloads worldwide, with a 5.0/5 rating in China.

For a product made by one person, staying alive is the harder part. It has been on the App Store for more than four years and is still updated; the latest version is 5.5, from November 2026.

What comes next

In progress: I’m adding at least three example sentences to every meaning of the 80,000 most common English words. Wiktionary’s own examples come first, generated ones fill the gaps, and a separate pass checks each one against its meaning.

Still on the list: an end-of-review count of how often you and the AI agreed, flip time as a silent signal, AI pronunciation practice, and a dark mode that looks right.

Next case study

AI-native product · 0 to 1 · Built with AI 拍拍出 Two photos, and a price for your old clothes that you can explain