AI interviewer · High-level system design
Whiteboard
that pushes back.
FabInterview runs a full HLD interview practice round: a real system design problem, an AI interviewer that questions your trade-offs, and a scored debrief when you put the marker down.
What you get
A full interview loop, not a chatbot with a prompt.
Interviewer
Follow-ups that probe
The AI challenges your choices the way a senior engineer would: capacity estimates, failure modes, trade-offs you glossed over.
Input
Speak or type
Talk through your design out loud, or type when you'd rather think quietly. Follow-ups are spoken back as well as shown in the transcript.
Library
Real problems
URL shorteners, WhatsApp, YouTube, Dropbox, Google Docs, crawlers, and the rest of the live set, across three difficulty levels.
Pressure
No hand-holding
The interviewer hands you the marker and stays quiet. No hints, no scaffolding, exactly like the round you're preparing for.
Debrief
Scored feedback
Every session ends with scores for requirements coverage, design quality, whiteboard usage, depth of reasoning, and communication.
Tracking
Progress over time
Session history and analytics show which dimensions are improving and exactly what to drill before the real loop.
How it works
Problem to debrief in one sitting.
1.
Pick a problem
Choose a question from the library and open the whiteboard.
2.
Defend your design
The interviewer clarifies requirements with you, then pushes on every decision while you sketch.
3.
Read your debrief
Scores, strengths, and the specific gaps to close before you sit the real round.
Pricing
Buy interviews, not a subscription.
One credit runs one full interview, debrief included. Nothing renews and credits never expire. 1 interview a day is free, without the debrief. Paid rounds are capped at 2 a day.
Free
1 interview a day
One round a day. The scored debrief unlocks when you buy credits.
- 1 interview a day, refilled at midnight UTC
- Any problem in the library
- Voice or text, with the full whiteboard
- Scored debrief
- Progress analytics
No card required
5 credits
Tune-Up · $3.80 an interview
A quick sharpen before a round that's already on the calendar.
- 1 credit = 1 complete interview, on any problem
- Full scored debrief on every round
- Deep-dive tiers, key moments, and a practice plan
- Credits never expire. No window to race
- Unlocks debriefs for the free interviews you already sat
Best for: An onsite you're already booked for
10 credits
Most popular
Sprint · $3.30 an interview
The full prep cycle. Enough rounds to close every gap you find.
- 1 credit = 1 complete interview, on any problem
- Full scored debrief on every round
- Deep-dive tiers, key moments, and a practice plan
- Credits never expire. No window to race
- Unlocks debriefs for the free interviews you already sat
Best for: A live interview loop
20 credits
Deep Prep · $2.45 an interview
Building the skill from the ground up, not cramming for a date.
- 1 credit = 1 complete interview, on any problem
- Full scored debrief on every round
- Deep-dive tiers, key moments, and a practice plan
- Credits never expire. No window to race
- Unlocks debriefs for the free interviews you already sat
Best for: Senior/staff loops, or starting cold
Every pack is the same product and the same complete debrief. The only thing that changes is how many interviews you get. Credits stack, so buying the small pack first never costs you anything.
Before you buy
Is this a subscription?
No. Every pack is a one-time payment for a fixed number of interviews. Nothing renews, there's no card on file to forget about, and there's nothing to cancel when your loop is over.
When is a credit spent?
The moment an interview starts, and only then. Browsing problems, re-reading a transcript, or opening a debrief you've already been given costs nothing. If a round fails to open, the credit goes straight back.
Do credits expire?
Never. That's the point of pricing this way. If your loop slips by a month, your credits are still sitting there. Whatever you don't use is waiting for the next time you're preparing.
Why a 2-interview daily cap?
Each round is a long, live conversation with a frontier model. 2 a day is well past what anyone can usefully absorb. It's there to stop one login serving a study group, not to slow you down. It never costs you credits, it just spreads them out.
What happens when I run out?
You drop back to the free tier. Your transcripts, debriefs, and analytics stay exactly where they are. You keep everything you've already earned, and topping up picks straight up where you left off.
Which pack should I buy?
Match it to how much runway you have. An onsite in a fortnight, take the Tune-Up. A live loop in progress, take the Sprint. It's what most people need. Starting from scratch or aiming at a staff round, Deep Prep gives you room to build the skill rather than cram. Buying small first costs you nothing: credits stack.
Still deciding?
Run today's free interview first. It's the whole interview, not a demo, and the scored debrief unlocks when you buy credits. You'll know inside ten minutes whether this is worth $33 to you.
Start free