Hey everyone 👋
I've been working on a platform called Cruscible and wanted to share it here because I think it fills a gap most coding platforms ignore.
The problem: You learn Python, you grind LeetCode, you get good at algorithms — but then at work, you're asked to build a rate limiter, a cache with TTL, a URL shortener, a notification router… and none of your practice prepared you for that and yes AI will help it out but without knowing the internals it will playout differently
Same with interviews — when asked to "design a rate limiter," most of us can whiteboard it. But could you actually code one that handles concurrent requests against a real Redis instance? That gap between "I can explain it" and "I can build it" is exactly what Cruscible is for.
What Cruscible does differently:
Instead of toy input/output problems, you implement real system designs in Python. Your code runs in isolated containers with actual infrastructure:
- Redis — build caches, rate limiters, session stores, pub/sub systems
- PostgreSQL — build URL shorteners, booking systems, payment gateways with real SQL
- Kafka — build message brokers, event-driven systems
- Key-Value stores, queues, S3 — and more
You get a contract interface (like RateLimiterContract with methods allow_request(), get_remaining_requests(), reset()), and you implement it. Your code compiles, runs against a real test suite, and gets scored on three dimensions:
- Functional — do your tests pass?
- Performance — can it handle 10K ops/sec?
- Code Quality — naming, structure, error handling
10+ LLD problems available right now and the total count spans 40+ — rate limiters, LRU caches, API gateways, distributed locks, cab booking systems, payment gateways, and more. All accepting Python.
DSA problems in Python are coming within days too — JSON parsers, CSV processors, expression evaluators, query builders — DSA patterns but in real-world contexts.
It's free. It's in beta. Built by a solo dev.
for those who want to test it out cruscible
Would love feedback from this community. What kind of problems would you want to see?