Whitepad
A mock interviewer that sees your whiteboard. Sketch, code, and defend your design in real time.
The Problem
You can't practice a system design interview alone.
System design interviews are conversations. A real interviewer watches your diagram take shape, interrupts with “what happens to that database at peak traffic?”, and pushes until they find the edge of what you know.
Practicing solo gives you none of that. You sketch boxes in silence, nobody challenges your choices, and you walk into the real thing having never once defended a design out loud.
Mock interviews with real engineers exist — at $100+ per session, on someone else's calendar.
The Approach
An interviewer that watches you work.
Whitepad pairs a whiteboard and a code editor with an AI interviewer that sees both in real time. As you sketch your architecture and write code, it follows along — asking clarifying questions, probing trade-offs, and pressing on weak points the way a senior staff engineer would.
When the session ends, you get structured scoring on your design, your reasoning, and your communication — not just a transcript.
How it works
A mock interview in three steps
- 01
Pick a problem
Choose from a bank of system design and coding questions — URL shorteners, feeds, rate limiters, and more.
- 02
Design out loud
Sketch on the whiteboard and write code in the editor. The interviewer sees every change and responds to what you're actually doing.
- 03
Get scored
Finish the session and receive a structured evaluation of your design choices, trade-off reasoning, and communication.
What Makes It Different
Practice that talks back
Sees Your Whiteboard
The interviewer reads your diagram as you draw it — questions reference the actual boxes and arrows on your board.
Sees Your Code
A full code editor sits beside the whiteboard. Write real code and get probed on it, just like on-site.
Staff-Engineer Probing
Not a quiz bot. Adaptive follow-ups that push on scaling, failure modes, and the trade-offs you glossed over.
Structured Scoring
Every session ends with an evaluation across design quality, depth of reasoning, and communication.
Practice on Repeat
No scheduling, no $100-per-session coach. Run a full mock interview whenever you have an hour.
Who it's for
Built for engineers with an interview coming
- Engineers prepping for senior and staff-level interviews where system design is the gate
- People who know the material but freeze when they have to defend a design out loud
- Anyone tired of passively watching system design videos instead of actually practicing
- Candidates who want reps against an interviewer that pushes back, on their own schedule
Your next interview is practice for free
Whitepad is live. Pick a problem, open the whiteboard, and run a full mock interview right now.