DevscapeIt 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.
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Devscape — system design interview practice
Stop reading system design. Start designing it.
Take a real interview question, draw the architecture yourself, and have it graded on the spot — so you find your weak spots here, not in the interview.
No signup required. Open a challenge and start designing in ten seconds.
27 challenges215 architecture checksInstant feedback
27system design challenges
215architecture checks behind them
12kinds of system
0signups, cards or limits
∞attempts, graded instantly
Practice
Know what you’re weak at before the interviewer does
27 system design challenges, each one carrying the checks an interviewer actually pushes on — 215 of them in all. Draw your answer, submit it, and get a score, the misses, and the follow-up question each miss would have earned you. Then fix it and go again.
No signup required. 8 beginner · 8 intermediate · 11 advanced · graded in your browser, signed out, as many times as you like.
How Devscape works
- 01Pick a challengeA real interview problem, with the real numbers attached — 500M tweets a day, 10:1 reads to writes, 100GB a user.
- 02Design the systemDraw the services, databases, queues and caches, and the connections between them. Links find their own way around.
- 03Submit itYour board is read as a graph and run against the challenge’s checks — in your browser, in about a second.
- 04Get your scoreWhat passed, what didn’t, the follow-up question each miss would have earned you, and how the model answer differs.
27 challenges, 215 checks, 12 kinds of system
Design a view counter7Design a comment system7Design search autocomplete8Design a distributed cache7Design a message queue7Design Airbnb9Design Yelp8Design Twitter10Design Google Docs9Design a payment system10Design an ad click aggregator9Design an LLM inference API9Design a RAG question-answering service10
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.
The difference
Not another diagramming tool
Excalidraw, Lucidchart, a whiteboard, a napkin — all of them let you draw a system. None of them tell you whether the system works.
| Aspect | Diagramming tools | Devscape |
|---|---|---|
| What you do | Draw a diagram | Design a system against a brief |
| When you finish | Nothing happens | It is marked, in seconds |
| Who says it is right | You do | A rubric that reads your graph |
| What a mistake looks like | You never find out | The question an interviewer would ask |
| The numbers | Not part of it | Capacity estimates graded too |
| What you leave with | A picture | A score, and a list of what to fix |
You can still just draw — the editor below is the whole of one, and it is free. It is simply not the reason to be here.
Who this is for
Backend engineers
You have built services. You have not had to defend a whole system out loud, against numbers, in forty-five minutes.
Senior engineers
You know the answer. This tells you whether the design you actually drew contains it — which is the thing being marked.
Candidates levelling up
SDE II, staff, and every rung where the round stops being about code and starts being about trade-offs and capacity.
People coming back to it
Years out from the last interview. Start on a pastebin, work up to fan-out at Twitter scale, at your own pace.
Twelve seconds
The board you’ll answer on
- 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 a box — or label a link.
- Drag a dot
- Connect two boxes.
- Click a line
- Select 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 do I practise system design interviews?
By designing systems, not by reading about them. Pick a challenge, read the brief and the numbers it comes with, draw the architecture on the board — services, databases, queues, caches and the links between them — do the capacity arithmetic, and submit. You get a score and a list of what an interviewer would have pushed on. The loop is worth repeating: attempt, read the misses, redraw, submit again. Passive reading is what leaves people stuck, because an interview tests whether you can produce a design under time, not whether you have seen one.
What system design questions are included?
All 27 of them are listed on the practice page and linked from the homepage. They run from a first pastebin, a URL shortener and a rate limiter up to Twitter’s timeline fan-out, WhatsApp, Uber, YouTube, Google Docs, a payment system and an LLM inference API — sorted beginner, intermediate and advanced, with the checks each one is marked against shown on the card.
How does Devscape grade your architecture?
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.
Can I practise without creating an account?
Yes — no account is needed and none is asked for. Open a challenge, draw the design, submit it and read the feedback, all of it signed out and with no limit on attempts. Signing in exists so your boards follow you to another browser, not to unlock anything.
Is Devscape 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.
Why not just draw the design in Excalidraw or Lucidchart?
You can, and nothing there will tell you the design is wrong. A drawing tool takes whatever you put on the canvas; it has no idea what the boxes mean, so it cannot notice that every timeline read goes straight to the database or that your write estimate is out by 40×. Here the board is a typed graph and the question comes with a rubric, so finishing the drawing is the point at which the work starts rather than the point at which it stops.
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.
Your next interview is a system design round.
Find out what you’d have missed while it still costs you nothing.
No signup required. The account is for carrying your boards between browsers, and nothing else is behind it.