A flashcard app with a streak counter is a weekend project. A spaced-repetition algorithm tuned against hundreds of millions of learner interactions, across dozens of professionally-designed courses, is a different scale of product entirely.
VIBE SCORE 95/100
A moderate score above just means the individual parts are buildable — it isn't a build/buy recommendation on its own. Here's the actual reason this one's still JUST PAY:
The parts this build actually needs, each rated on its own — the average is the Vibe Score above.
| Landing page | 99 |
| CRUD database | 95 |
| User login | 92 |
Two real costs, not just "free": the AI agent's own usage, and hosting once it's running. Both are estimated from this app's own effort rating and component list — see the assumptions on the method page.
| AI agent — with a subscription (Claude Pro/Max, Cursor, etc.) | $0 marginal |
| AI agent — pay-per-use API, no subscription | $86–$172 one-time |
| Hosting, once it's running | $0/mo (free tier) |
| Domain name, if you want your own | ~$12/yr |
Duolingo costs $6.99/mo. Even paying per-token with no subscription, and accounting for hosting, this build pays for itself in about 25 months.
Don't feel like building it? These are already made, open-source, and free.
Just pay. A flashcard app with a streak counter is a weekend project. A spaced-repetition algorithm tuned against hundreds of millions of learner interactions, across dozens of professionally-designed courses, is a different scale of product entirely.
Duolingo costs $6.99/mo (about $84/yr) as of 2026-08. That's what a working rebuild would save you.
Course content for a full language, professionally designed and pedagogically sequenced, represents years of curriculum work you'd need to either license or write yourself Their spaced-repetition algorithm is continuously tuned against a genuinely massive dataset of real learner performance — that's applied research, not a formula Speech recognition for pronunciation practice adds real ML complexity beyond text-based quizzing
Yes — Anki are open-source options worth trying before you build your own. Details are in the standard parts section on this page.
Closest matches on the register — ranked by the build parts they share with Duolingo, not just by category.
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