Live engine — runs in your browser
Don't defend your design.
Run it.
Design systems stage by stage, then execute them — request-level traces show where the latency goes and where the design breaks. An AI staff engineer reviews every stage.
One problem, end to end
The sim above is one slice of URL Shortener. The full problem:
- 01
Scope it
9 guided stagesRequirements → capacity → API → data model → HLD → trade-offs.
- 02
Do the math
5 derivationsCapacity math from the stated traffic inputs — QPS, storage, bandwidth.
- 03
Choose the store
6 options comparedDatabase trade-offs argued, not asserted.
- 04
Draw and wire it
10-node reference HLDNodes carry internals, edges carry contracts — the metadata the engine reads.
- 05
Run it, break it
5 traces + chaosCDN hit/miss tiers, async click fan-out, kill-the-leader drills with RTO/RPO verdicts.
- 06
Defend it
3 predict gates · 5 deep-divesCall the outcome before the engine reveals it; an AI staff engineer reviews every stage.
Go deeper
The simulator above is the front door. Behind it:
81 system design problems
Designed stage by stage in the full editor — and every one ends with your diagram executing.
URL ShortenerRate LimiterTwitter / X TimelineWeb Crawler+77 moreBrowse problems250 running scenes · build the infra itself
20 build-it-yourself curricula — step inside the internals and predict what happens before it does.
KafkaRaftRedisS3-style object storeLSM-tree engineCDN+14 moreBrowse scenesStory Mode: a year on call
Join Ledgerline, a payments fintech, as the infra hire — every shortcut you take becomes debt that comes back to find you.
11 production crises3 quiet monthsdebt that maturesStart season oneStop defending designs. Start running them.
The demo above is live — no signup, the engine runs in your browser.