How to Build a Flashcard App with Spaced Repetition

Build a flashcard app people actually study with: decks, cards, a review queue, spaced repetition scheduling, imports and a fast phone-first review screen.

Mythex Team · 2026-09-29 · 5 min read

A flashcard app is decks of cards, a review screen that flips each card, and a scheduler that decides which cards you see today. The scheduler is what separates a useful study tool from a digital pile of index cards: with spaced repetition, cards you know come back rarely and cards you struggle with come back soon. Build the review screen and a simple scheduler first; add imports, images and audio after.

What a flashcard app needs

Data

Table	Fields
Decks	Owner, name, description, public or private
Cards	Deck, front, back, optional image or audio, tags, created date
Card state	User, card, due date, interval, ease or difficulty, repetitions, lapses
Reviews	User, card, time, rating (Again / Hard / Good / Easy), time taken

Keep card state separate from the card itself. If decks are shared, two people studying the same card each need their own due date. Keep every review too: it's the history you'll need to improve the scheduler, show progress charts, or switch algorithms later.

Choosing a scheduling method

You don't need to invent anything here. Three well-known approaches:

Method	How it works	Good for
Leitner boxes	Cards move up a box when right and back to box 1 when wrong; each box is reviewed less often	Simplest to build and explain
SM-2	Each card has an interval and an "ease" that grows or shrinks with your rating	Proven, widely copied, easy to test
FSRS	Models how likely you are to remember each card and schedules for a target retention	More accurate; Anki offers it as an option

For version one, pick Leitner or SM-2. Write the rules into your prompt with a worked example, such as: "A new card rated Good is due in 1 day, then 3 days, then roughly 2.5 times the previous interval each time it's rated Good. Rated Again, it's due again in 10 minutes and its interval resets."

Whatever you choose, ask the AI to put the scheduler in one separate function with tests. Then you can swap it later without touching the rest of the app.

Decisions to make

Whose day is it? "Due today" should follow the user's time zone, and many study apps let the day roll over at an hour like 4 am, so a late-night session counts as the same day.

Daily limits. Without a cap on new cards per day, an eager user adds 500 cards and faces an impossible review pile a week later. Default to something modest and let people change it.

Card types. Basic front/back first. "Reverse" cards (also test back to front) and cloze deletions (fill in the blank in a sentence) are popular, but each adds rules. Add them when basic works.

Shared decks. A teacher sharing a deck with a class is a great feature and a permissions question: students study it but can't edit it, and edits by the teacher should reach everyone without resetting their progress.

Offline. People study on trains and planes. A progressive web app can cache today's cards, but syncing reviews from two offline devices is genuinely hard. Online-only is a fair first version. Our guide to native vs progressive web apps explains the options.

A first prompt that works

Build a flashcard web app designed for phones first. Users log in and create decks, and add cards with a front and back (text, with optional image). Each user has their own review state per card: due date, interval, ease, repetitions and lapses. Use the SM-2 algorithm: ratings Again, Hard, Good, Easy; Again resets the interval and shows the card again in 10 minutes. Put the scheduler in its own tested function. The review screen shows the front, a large "Show answer" button, then four large rating buttons. "Due today" uses the user's time zone with the day starting at 4 am. Limit new cards to 20 per deck per day by default. Log every review. Show a deck list with due counts and a simple stats page of reviews per day. Add CSV import with front and back columns. Save everything in a database.

Build steps

Decks and cards. Create two decks and twenty cards. Check how quickly you can add a card.
Review screen. Study on a phone. It should feel instant; any delay between cards is felt hundreds of times a day.
Scheduler tests. Give the AI a table of rating sequences and expected intervals, and check the results. Then change your device clock or ask for a test mode to simulate the next few days.
Daily limits and time zone. Review late at night and confirm the next day's queue is right.
Import. Import a real CSV of a few hundred cards and check special characters, commas inside cards and line breaks.
Stats. Reviews per day and upcoming due counts. Keep charts simple.
Extras. Images, audio for language cards, reverse cards, shared decks — one at a time.

Common mistakes

Storing the due date on the card. It must be per user.
Throwing away review history. You'll want it for stats and any future scheduler.
No new-card limit. Users burn out in a week.
Tiny buttons. Rating happens one-handed; make the buttons large and far apart enough to avoid mis-taps.
No undo for the last rating. Mis-taps happen daily.
Server time for "today". Use the user's time zone.
Resetting progress when a card is edited. Fixing a typo shouldn't send a mature card back to the start.

When a ready-made product is the better choice

If you just want to study, mature flashcard apps already exist, several of them free, with years of work on scheduling, sync, offline use and shared decks. Anki in particular has a huge library of community decks. Use them.

Build your own when the cards are part of something bigger: a course you sell where flashcards reinforce each lesson, a language school giving students decks tied to its syllabus, a company teaching staff product knowledge, or a subject with card types the general tools handle badly. You own the content, the design and the student data. Pair it with a quiz app for tests, or build it into an online course platform.

Building it with Mythex

Mythex builds this as a web app you can open on any phone and add to the home screen. Describe the app in chat, check the review screen in the preview's phone-size frame, and ask for accounts and saved progress — Mythex adds a dedicated database when the app needs it, and file storage if cards have images or audio. Native App Store and Google Play apps are coming soon on Mythex and aren't available today. Use Ask mode to have the agent explain its scheduling function before you trust it, and publish to a mythex.ai link when it works.

Questions

What is spaced repetition?

Spaced repetition shows a card again just before you are likely to forget it. Cards you know well come back after longer and longer gaps; cards you miss come back soon. It makes study time go further than reviewing everything equally.

Which spaced repetition algorithm should I use?

For a first version, a simple Leitner box system or SM-2 is enough and easy to test. FSRS is a newer, more accurate scheduler that Anki offers as an option; it is worth considering once you have review history to tune it.

Can a flashcard web app work offline?

Partly. A progressive web app can cache the app and the day's cards so reviews work without a connection, then sync when it reconnects. Syncing reviews made on two devices while offline needs careful merge rules, so many first versions stay online-only.

Can I build a flashcard app without coding?

Yes. An AI app builder can create decks, cards, the review screen and the scheduling from a description. Give it worked examples of the scheduling rules and check them, because that logic decides whether the app helps people learn.