The technical interview sandbox

Build the instinct to design under pressure.

A focused workspace for the decisions that separate a diagram from a production-ready system. Practise, defend, learn what you missed.

Interactive design canvas Adaptive follow-ups Clear readiness signal
Interview room
44:12 remaining
API gateway
Checkout svc
Orders DB
Safety compiler active6 nodes · 5 wires

Shadow interviewer

What happens when payment times out after inventory is reserved?
Make the consistency model explicit.

Signal so far · 68/100

Not another course. A place to build the reflex.

A better feedback loop

Experience is the curriculum.

The fastest way to become better at design is to make decisions, encounter the sharp edge, and understand the trade-off.

01

Practise the shape

Use a real canvas, not a blank text box. Map boundaries, data, and dependencies.

02

Defend the choice

A shadow interviewer asks the counter-question your diagram is avoiding.

03

Close the gap

Leave with a score, concrete next steps, and a better prompt for tomorrow.

One workspace, three lenses

Zoom in without losing the system.

Move from high-level boundaries to database constraints to low-level abstractions. Your design stays connected as you go deeper.

HLD

Shape the system

Services, gateways, queues, caches, and failure paths.

ERD

Model the truth

Tables, keys, indexes, constraints, and consistency.

LLD

Make it buildable

Classes, interfaces, methods, and patterns.

A clear path to ready

Know what to practise next, not just what you got wrong.

Your readiness map grows from the quality of your decisions: system boundaries, data choices, failure modes, and how clearly you communicate them.

Requirement clarity

You make the unknowns explicit before drawing infrastructure.

Trade-off quality

You can explain why this choice wins under these constraints.

Failure handling

You have a credible answer when the happy path breaks.

Readiness map

Updated after each interview

68
System design74/100
Database design61/100
Low-level design48/100

Strong fundamentals · next: failure modes

Your next design is waiting

Practise until good decisions feel like second nature.

Start for free