What do you want to understand today?
First run a sample with a known bug
- Open Dry run and press Fill in a sample
- Dry run it: Dryrun runs the code and records every step
- Press play, then press Why did it fail?
The sample counts as one of your daily runs.
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Paste a problem and your code. Dryrun runs it, records every step, and animates the run.
Dry run a solution
Paste the problem and your solution in Python, Java or JavaScript. Claude Code works out how to call it and what to draw; the tracer runs your real code.
My runs
Every dry run you've started, newest first.
Compare two solutions
Same inputs, two runs: which one does less work? Steps are real recorded operations, so the ratio is an empirical measure of complexity.
Press ▶ to watch the run, or use ← →.
System design
Lessons that build real architectures up one piece at a time, follow a request through them, and break them on purpose, drawn from engineering write-ups.
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Lesson notes
Trade-offs, glossary, numbers, quiz, ask, practice
AI-generated, can be wrong.
AI-generated, can be wrong.
Before you read on, sketch how you would build this: the main components, how a request flows, where the data lives, what breaks first. Write it or draw it, then get interviewer-style feedback against the lesson.
Back-of-the-envelope arithmetic, the way an interview starts. The sliders begin at this lesson's numbers; move them and watch what a 10× change does to the storage, the QPS and the node count.
Thirty-five minutes with Claude as the interviewer: requirements, estimation, high-level design, a deep dive and trade-offs, then a scorecard. It knows this lesson's design; you don't get to peek.
Review
Flashcards from the lessons you added, scheduled by spaced repetition: what you get right comes back later, what you miss comes back tomorrow.
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Permanently deletes your account, your dry runs, progress, bookmarks and feedback. Shared links stop working. This cannot be undone.
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Newest first. Drafts expire after 48 hours.
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Admin
Who's using Dryrun, what it costs, and whether Claude Code is healthy.