Diagrams for System Design Interviews

A repeatable drawing order

Interviewers watch how you think as much as what you draw, so use the same order every time. Clarify requirements and write them down in a corner. Sketch the simplest end to end path: client, server, database. Then add the parts the requirements force on you, one at a time, and say why before you draw each one.

Do the numbers on the board

Write requests per second, storage per year and read to write ratio next to the picture. They justify the boxes you add. A cache appears because reads outnumber writes by a hundred to one, not because every diagram has a cache. Back of the envelope maths in the margin is also easy for the interviewer to correct kindly.

Leave room and label the arrows

Start in the middle left and leave space on the right, because the design will grow. Label arrows with the call or the data, for example write post or fetch feed. A box with no labelled arrows is a guess; a box with a label is a decision.

Practise with templates

Open a template such as the URL shortener, redraw it from memory on a blank page, and compare. The goal is not to memorise a design but to make drawing the building blocks fast, so your attention stays on the trade-offs. Because ArchBoard works offline in your browser, you can practise anywhere without an account.

Handling questions

When the interviewer pushes on a choice, resist redrawing everything. Point to the box, state the trade-off in one sentence, and amend the picture only if the answer changes the design. A calm edit, such as adding a replica or a queue, shows you can adapt without panicking, and the history of small changes tells the story of how your reasoning evolved.

Try it with a template

• URL Shortener
• Chat Application
• News Feed
• Rate Limiter