Pay once. Pass.
No subscriptions, no upsells, no per-feature paywalls. Plinth Pro is a one-time purchase. Your account doesn't expire — it just keeps getting better as we add more questions.
- Full 1207+ question pool, growing every cycle
- Unlimited mock exams (60Q · 120-min · official domain weighting)
- All 493+ Leitner flashcards with reverse-mode
- Adaptive weak-spot drills built from your answer history
- Lifetime dashboard, history, per-domain mastery, score projection
- 19-section Compendium + Stem Decoder + Modules library
- Cross-device sync (web + mobile)
- Mobile app coming soon — included
Secure checkout via Stripe · USD · Try the free preview · All sales final · Grandfathered into every future update.
Native mobile app launching to the iOS and Android stores. Pricing is higher there because Apple and Google take a 15–30% cut. Web purchase already includes mobile access if you'd rather save $5 — your account syncs across both.
Anonymous trial vs Plinth Pro.
Try 20 questions free as a guest. When you're ready for the real prep, Plinth Pro is one-time $20 — your account is created automatically from your purchase email.
| Feature | Free | Plinth Pro |
|---|---|---|
| Practice questions | 20 (anonymous) | Full 1207+ across 13 scenarios |
| Mock exams | Locked | Unlimited · Standard + Comprehensive modes |
| Stem Decoder hints | Limited preview | 100% coverage · L1 pointer + L2 pattern reveal |
| Flash cards | Locked | All 493+ cards · Leitner spaced repetition |
| Weak-spot drills | Locked | Adaptive, unlimited |
| Dashboard + hint analytics | Locked | Where you used hints, by scenario × level |
| Languages | EN | EN · 한국어 (questions, hints, chrome) |
| History + lifetime sync | Locked | Web + mobile cross-device |
| Future updates | — | Grandfathered for life — no upgrade fee |
| Account | None — anonymous trial only | Created automatically from your email |
Before you buy.
Is $20 really one-time, or do you renew?+
Truly one-time. No subscription, no auto-renew, no card stored after the purchase. You own your account.
What if I buy on web but want mobile too?+
Web purchase includes mobile access at no extra cost. Sign in on the mobile app with the same email — your progress and Pro status sync automatically. The $25 mobile-store price exists only if you buy directly through the App Store / Google Play instead of the web.
What's the refund policy?+
All sales are final — but you can try the full preview free before buying, so you know exactly what you're getting. Once you're in, you're in for life: every new question we add, every new feature we ship, every Stem Decoder amendment — you get it all, no extra charge, no upgrade fee. Use the free preview to decide; once you buy, focus on passing.
Will the price go up?+
Maybe — we've kept it at $20 so individual engineers can self-fund. Lock in today; if we raise the price later, your account isn't affected.
How does payment work?+
Standard Stripe Checkout. Card or Apple Pay / Google Pay. After payment your account is upgraded immediately via webhook — no waiting.
Can my employer expense this?+
Yes. Stripe sends a tax invoice to the email used at checkout. Most teams reimburse one-time exam-prep tools without issue.