System Design Assist · Mac
Design the system while they’re still describing it.
Numbers first, like a senior engineer: users, QPS, storage. Then a clean architecture diagram on a private whiteboard, and a written walkthrough you can talk through box by box.
- Estimates from the conversation
- Diagram you can redraw
- Hidden from screen share
Interviewer asked
Design a URL shortener for 100M new links a day.
▍
See it draw
From “design a URL shortener” to a whiteboard in seconds.
Back-of-the-envelope
- Daily active users
- 50M
- New links / day
- 100M
- Write QPS
- ≈ 1.2k
- Read QPS (10:1)
- ≈ 12k
- Storage / year
- ≈ 18 TB
- Cache (hot 20%)
- ≈ 10 GB
The numbers fill in from what the interviewer says. Type over any of them, then draw: the diagram uses yours.
How it works
Back of the envelope, then the boxes.
01
Generate Diagram
Press it under any design answer, or in Deep Thinking. The copilot decides which estimates this system needs.
02
Estimates fill in
DAU, QPS, sizes and retention are read from the conversation. Type over any value; auto-answers wait while the panel is open.
03
Draw with estimates
The diagram, an estimates panel and the QPS and storage working appear under your answer. Or skip straight to the drawing.
QPS & storage math
The working is shown, so you can say how you got the number.
Hand-drawn whiteboard
A diagram that looks drawn, not pasted, below the written answer.
Redraw with new info
“Add a queue between the API and the DB.” The diagram changes, not restarts.
Copy Diagram
Copy it as an image for a shared whiteboard or doc.
Stays pinned
The diagram stays on screen until you move to the next question.
Mutes while you present
The mic pauses when the diagram opens, so your own walkthrough isn’t treated as a question.
Deep Thinking
For a hard design, generate a deeper answer from the whole conversation on demand.
Your project, ready
Current Project shows your own architecture and talking points for “tell me about something you built”.
System Design Assist questions
What does System Design Assist do in a live interview?
When the interviewer asks you to design something, press Generate Diagram. The copilot works out the estimates the design depends on, then draws the architecture as a diagram on a whiteboard panel under the written answer, all on your screen only.
Where do the estimate numbers come from?
For each design it lists the 5–7 numbers that matter (daily users, QPS, object sizes, retention…). Values fill in from what the interviewer says, a couple of seconds after each new line. Anything you type wins.
Can I change the diagram when the interviewer adds a requirement?
Yes. Redraw takes typed instructions such as “add a CDN and make writes async” and updates the existing diagram instead of starting over.
Can I share the diagram?
Copy Diagram puts it on your clipboard as an image, so you can paste it into a shared whiteboard or doc if the interviewer asks you to draw.
Is it on Windows?
System Design Assist is in the Mac app today (version 3.0 and later). The Windows app has live answers, coding help and screen-share protection; diagrams are coming.
Which plan includes it?
The Standard plan, $149/month, with no limit on sessions. The free trial includes one 30-minute live session.
Two ways to start.
Live Interview Assist
Answers in the room. Invisible on the share.
- Behavioral, coding and system design rounds
- Hidden from screen share and recordings
- Mac and Windows · phone mode with no install
AI Auto Apply
Applications go out while you prepare.
- Matched to your resume, with reasons
- A tailored resume for every job
- You approve, or let it run inside your limits