It reads the board, not a checkbox
Your design is a typed graph, so the marking is graph questions: is there a cache on the read path, does the client reach the store without passing a service, is the write path async.
New26 system design questions — drawn, then graded→
The workspace for software architecture
Your software architecture, in one place
A box for every moving part, a line between them, and links that work out their own way around.
No account needed. Boards stay in this browser until you want them anywhere else.
26questions, graded
6types to start with
3worked examples
3ways out: PNG, SVG, JSON
0accounts required
Practice
Every other diagramming tool stops when you stop drawing
This one marks the board. 26 system design interview questions, 205 checks between them, and a score the second you submit — with the question an interviewer would have asked about everything you left out.
8 beginner · 8 intermediate · 10 advanced · graded in your browser, signed out, as many times as you like.
- 1Pick a questionBriefs with the real numbers attached — 500M tweets a day, 10:1 reads to writes, 100GB a user.
- 2Draw the answerThe board you have already seen. Boxes, links that route themselves, your own types.
- 3Do the arithmeticThe capacity numbers, and the two or three things you would have said out loud.
- 4Submit itMarked where you stand: a score, every check, and what the model answer has that you don’t.
26 questions, 12 kinds of system
Every miss is a follow-up question
Nothing comes back as “incorrect”. It comes back as the question an interviewer would have put to you, with the answer they were listening for underneath it.
The arithmetic is marked too
Capacity estimates are graded by order of magnitude — within 3× either way, because being out by 40× is the mistake worth catching and nobody cares about 15%.
Held against a model answer
Every question ships with the design an interviewer had in mind, compared to yours box by box and link by link. Differing from it is allowed; not knowing you differ isn’t.
Twelve seconds
Watch one come together
- 1Drop a box
- 2Drag a link off it
- 3Move it — the link follows
- 4Share the lot
The palette
Types you invent yourself
6 to start with, and none of them sacred. Name your own, give it a colour, drag it where it belongs — and the palette belongs to that board alone, not to the app.
The links
Lines that route themselves
You say what connects to what. Where the line goes, and what it steps around on the way, is not your problem.
Boards
One for every system in your head
Name them, switch between them, rename or delete them — most recently touched at the top. Each keeps its own diagram and its own palette, so none of them has to agree with the others.
Sharing & export
Send the diagram, not a screenshot
A link anyone can open, read only, switched off whenever you like. Or a file — and the file is drawn from the board, not scraped off the screen.
Everything else in the box
It saves itself
Half a second after you stop.
Start as a guest
Sign in later; your boards come with you.
Undo means undo
Ctrl+Z for a box, a toast for a board.
Bring one in
Paste the JSON, or pick the file.
Save a copy
Fork any board someone shares with you.
Say when it breaks
One click away, and you see the reply.
Or start from one that already works
Simple web app
URL shortener
Instagram feed- Blank board
Shortcuts
Ten things, and you know the whole editor
- Drag
- Move a box. Links follow.
- Double-click
- Rename in place.
- Drag a dot
- Connect two boxes.
- Click a line
- Delete that link.
- Del
- Remove the selection.
- CtrlZ
- Put the last thing back.
- F
- Frame the whole design.
- Ctrlscroll
- Zoom around the pointer.
- Two fingers
- Scroll the board.
- ?
- This list, on the board.
Boards you can get back
Deleted is not destroyed
A board is stamped, not dropped.
Sharing is a decision
Private until you say so. Revocable after.
Read-only means read-only
They get the picture, never the editor.
Your work leaves with you
JSON out, JSON back in.
Before you start
How does the grading work?
Your board is a typed graph, so most of what an interviewer pushes on is a question about it: is there a cache on the read path, does the client reach the store without passing through a service, is the write path async, is that capacity estimate the right order of magnitude. Those checks are run over your design in the browser the moment you submit. The same design always scores the same, and anything that cannot be checked is left out of the score rather than guessed at.
Do I need an account to practise?
No. Open a question, draw the design, submit it and read the feedback — all of it works signed out, with no limit on attempts. Signing in exists so your boards follow you to another browser, not to unlock anything.
Is it free?
Yes. There is nothing to buy, no per-attempt cost and no trial. The grading runs on your machine, which is most of the reason it can be.
What do I get back when I submit?
A score out of 100, every check that passed with the evidence from your board, every check that failed written as the question an interviewer would have asked, the answer they were listening for, and a comparison against the model answer — which boxes and links it has that yours does not.
How is this different from reading system design articles?
An article tells you the answer. Here you draw one first and then find out what you left out, which is the part an interview actually tests. The brief comes with real numbers, the capacity questions are marked, and the follow-ups arrive after you have committed to a design rather than before.
Contact
Say it here
A question about the practice questions, something about your account, or anything the FAQ above didn’t answer. It goes to a person, not a queue — there is nobody else here.
- No account needed
- Leave an address and the reply goes there, and nowhere else.
- Signed in?
- Skip the details — the reply lands on your messages page.
- Found a bug instead?
- Report it — that form brings the board you had open with it.
Open a board. It’s already ready.
Nothing to install, nothing to configure, nothing to sign up for.