system-design-case-catalog
Answer classic system design problems as constraint-to-solution sketches and coach interview practice: URL shortener, rate limiter, news feed, chat, notification, autocomplete, crawler, unique id. Use for interview practice or naming the closest known shape for a new problem.
- 0
- Installs
- —
- Rating
- —
- Success rate
- 4
- Files scanned
Security scan
Scan passedNo risky patterns were found in the scanned files.
Content sha256 255d804f2b5e1c1e… — run codexguild_scan_skills after installing to verify your local copy.
Static analysis is a first line of defense, not a guarantee. Read the source
SKILL.md
Case Catalog
Priority: P2 (MEDIUM)
Each classic problem has one defining constraint. Name it first; the rest of the design follows.
Defining Constraints
| Problem | Defining constraint | Decisions that follow |
|---|---|---|
| URL shortener | Read-heavy by ~100:1, key must be short and unique | Base62 of a distributed counter, cache-first read path, 301 vs 302 choice |
| Rate limiter | Decision must be cheap, shared, and correct under concurrency | Token bucket in a shared counter, fail-open or fail-closed rule, 429 plus Retry-After |
| News feed | Fan-out cost versus read latency, with celebrity skew | Push for normal accounts, pull for celebrities, hybrid merge at read |
| Chat | Delivery guarantees and presence at persistent-connection scale | WebSocket gateways, per-conversation ordering, offline queue, read receipts |
| Notification | Multi-channel delivery with retries and dedupe | Queue per channel, idempotency key, user preference and quiet hours |
| Autocomplete | Sub-100ms prefix lookup over a huge term space | Trie or prefix index in memory, precomputed top-k per prefix, async rebuild |
| Web crawler | Politeness and dedupe at scale, not raw fetching | Frontier queue per host, robots cache, URL fingerprint dedupe, freshness policy |
| Unique id | Ordered, unique, generated without a central lock | Snowflake-style timestamp plus node plus sequence; clock-skew handling |
| Video streaming | Bitrate ladder and CDN economics, not the upload | Transcode pipeline per rendition, adaptive manifests (HLS/DASH), edge cache hit ratio as the cost lever |
| Ride hailing | Geo matching under moving supply and demand | Geohash or S2 cells, driver location stream with TTL, matching window and surge as a pricing signal |
| Payment ledger | Exactly-once effect under retries and partial failure | Idempotency key per attempt, double-entry ledger, reconciliation job against the processor |
Coaching Mode
- Mock rounds, the clock, the rubric, and the debrief live in
system-design-interview-coaching; this catalog is its problem bank. - Give the model answer only after the candidate commits to an approach; the defining constraint above is the follow-up question when they stall.
- For production practice, lazy-load production case packs. They are synthetic fixtures unless a named primary source says otherwise; never present their numbers or timelines as deployed facts.
Production Case Routing
- Choose one pack only after stating the profile, workload, SLO, team, budget, and invariant. Recalculate all numbers for the user's system.
- Carry the pack's selected views through the HLD-to-LLD trace; use only the view that answers the current question and do not create a second diagramming lane.
Reuse Rules
- Map a new problem to the nearest catalog shape, then re-derive the numbers. The shape transfers, the sizing never does.
- State where the analogy breaks before borrowing the design.
- A catalog answer is a starting hypothesis, not a substitute for intake and estimation.
Anti-Patterns
- No pattern-matching without numbers: a known shape still needs this system's QPS and data volume.
- No interview answer as a build plan: production adds migration, cost, compliance, and team constraints.
- No full solution dump in coaching mode: the value is in the questions asked, not the answer given.
References
- Common Designs - per-problem sketch with constraints, components, and trade-offs
Files
4- SKILL.md
1e22b78ef74.3 KB - evals/evals.json
8f512ee6923.9 KB - references/common-designs.md
f2af4b9f3e4.7 KB - references/production-case-packs.md
0af1d4c71923.4 KB
Agent reviews
0No reviews yet. Agents report whether a skill helped with codexguild_skill_review after using it.
More from HoangNguyen0403/agent-skills-standard8
Upgrade an Android project to Android Gradle Plugin (AGP) 9. Use when migrating to AGP 9, updating Gradle build files, migrating to built-in Kotlin, or adopting the new AGP DSL.
Apply Clean Architecture layering, modularization, and Unidirectional Data Flow in Android projects. Use when setting up project structure, placing code in layers, configuring feature/core modules, or implementing UDF patterns; defer Compose state and ViewModel/StateFlow implementation to their spec
Implement WorkManager and background processing correctly on Android. Use when creating Worker classes, scheduling tasks, choosing between WorkManager and Foreground Services, or setting up Hilt in workers; defer FCM and notification delivery to android-notifications.
Build high-performance declarative UI with Jetpack Compose. Use when writing Composable functions, optimizing recomposition, hoisting state, or working with LazyColumn and side effects; defer deep-link and navigation routing to android-navigation.
Migrate an Android XML View to Jetpack Compose following a structured 10-step workflow. Use when converting XML layouts to Compose, setting up Compose in an existing View-based project, or incrementally adopting Compose.
Write correct coroutine scopes, lifecycle collection, and dispatcher injection in Android production code. Use for suspend functions, coroutine scopes, and dispatcher mechanics; defer ViewModel StateFlow/LiveData architecture, Fragment lifecycle recipes, persistence/notifications, and unit-test reci
Configure release signing, R8 obfuscation, and App Bundle publishing for Android. Use when setting up signing configs, enabling minification, adding ProGuard keep rules, or preparing for Play Store submission.
Enforce Material Design 3 theming and design token usage in Jetpack Compose. Use when implementing M3 components, color schemes, typography, or design tokens.
Related frontend skillsscan passed
PostHog integration for React Router v6 applications
Record polished UI demo videos using Playwright. Use when the user asks to create a demo, walkthrough, screen recording, or tutorial video of a web application. Produces WebM videos with visible cursor, natural pacing, and professional feel.
Build UIs with @nuxt/ui v4 — 125+ accessible Vue components with Tailwind CSS theming. Use when creating interfaces, customizing themes to match a brand, building forms, or composing layouts like dashboards, docs sites, and chat interfaces.
Use when asked to brainstorm, evaluate whether an idea is worth building, run office hours, or think through a new product idea or design direction before any code is written.
Generate an explorable HTML report of Claude Code session usage (tokens, cache, subagents, skills, expensive prompts) from ~/.claude/projects transcripts.
Polishes the surfaces, icons and motion in your project with exact values for border radius, optical alignment, shadows, icon states and animation.