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Free system design tools
Small tools for the sums a system design interview asks for. Each one shows its working in plain words, so you learn the method and not just the answer.
Capacity Estimator
Type in your users and your data. Get requests per second, storage, bandwidth and a server count, with every sum written out.
You type: daily active users, requests per user, read:write ratio, item size, how long you keep data.
You get: requests per second (average and peak), storage per day and per year, bandwidth, cache memory, a rough server count.
Open the Capacity Estimator
The tools teach one sum each. The System Design course teaches the whole design, and the interview guides show the sums on real questions.