Learn software design in order. Plan it around your week.

54 system design problems in five timed phases on a whiteboard. Score each phase against a reference answer and watch your scores over time. Free account required to run one.

A canvas with architecture stencils for load balancers, caches, queues and databases. Export to PNG, SVG or .excalidraw.

32 problems from a toast and a modal up to a Trello board and a real-time chat. Each one starts with the problem statement, explains the solution, and runs right here in a live preview.

Every SQL practice problem has a Try it box. Your query runs on the problem's own tables in the browser, and Check answer tells you what is off.

Streaks, weekly activity, practice scores and the revision ladder, built from what you already do. Weak tags come first, with what is holding each one back.

Patterns and SOLID topics with before and after code open in a side by side diff, file by file, with unchanged lines folded away. Press ⌥D in the editor.

Set the text size, line width and line spacing of every note. Hover a linked topic to see what it covers and whether you have read it. On a phone, the main actions follow you down the page.

Complete a topic and open the next in one press, or step along the path with J and K. Already know a track? Mark it all done at once, with undo.

Pick a number of topics or minutes of reading and watch the ring fill. The revision queue shows how many reviews land on each of the next fourteen days.

Rate each question Missed, Partly, Got it or Easy. The FSRS scheduler brings it back just before you would forget, at the recall target you pick, and Insights lists the cards you miss most.

Write your stories as Situation, Task, Action and Result, see which common questions still have no story, and tell them out loud against a timer.

Query a small shop database in the browser, browse its tables, save the queries you like and reset it whenever you want a clean start.

Press L and the browser reads the note aloud. Share a link to any passage you select, and watch the minutes left as you read.

Group topics into lists such as Amazon loop or Weak areas, and save any topic to one straight from its page.

Due cards, topics to recall, one story out loud and today's plan and planner tasks, in one pass with one progress bar. Turn off any step you want to skip.

Press N on any topic and your note and highlights open in a panel next to the text. Type [[ to link another topic, and each topic lists the notes that link to it.

Get a read-only link to a card with your topics done, streak and progress per track, or download it as an image. Stop sharing and the link stops working.

Send a link and your partner follows your clock, reads the reference answer and scores you on their own screen. No account needed on their side.

Record each interview phase or a story out loud, then play it back. Stories show how long each STAR part took against a suggested split. Recordings never leave your browser.

The reference stays hidden while you draw. Then check your board to see which parts you got and which ones to study.

Fresh storage, traffic, bandwidth and server problems every round, graded by how close you got, with the working shown and a cheat sheet of numbers worth knowing.

Select a few words and press Fill in. The sentence becomes a practice card with those words blanked out.

Pin the tracks you are studying and only they show under Topics, each opening to its sections. Filter by To read, In progress, Due or Saved, and hide the pages you never use.