Browser-based system design simulator. Drag components onto a canvas, wire them up, drive traffic, inject failures, watch real-time metrics.
Not a diagramming tool. Architectures actually run.
- 23-kind component catalog — clients, CDN, WAF, LB, services, caches, databases, queues, event bus
- Live metrics — per-node throughput, p50/p99 latency, in-flight, queue depth, error rate, sparklines
- Chaos injection — kill nodes, slow them down, drop packets
- Traffic control — 1 → 1,000,000 rps, 0.25x → max speed
- Topology lint — 9 rules, anti-pattern chips, worst-p99 diagnosis
- Cost + SLO chips — per-node $/mo + p99 budget
- Templates + scenarios — 13 starter architectures, 6 scripted drills
- Export / import as JSON
Built for system design interview prep, architecture validation, and teaching distributed systems.
Prereqs: bun, Go 1.22+, TinyGo.
cd apps/web && bun install
cd .. && make sim
cp $(tinygo env TINYGOROOT)/targets/wasm_exec.js apps/web/static/
cd apps/web && bun run devOpen http://localhost:5173. Drag a Source → Service → Database, click Run.
make sim-go # standard Go build (~2MB, full stdlib)
make clean
cd apps/web && bun run typecheck && bun run lint
cd sim && go test ./... && go vet ./...SvelteKit 2 + Svelte 5 runes · @xyflow/svelte · Tailwind · Go → TinyGo → WASM (~200KB) · Web Worker host · Vercel static deploy. No server — sim runs in your browser.
Empty canvas — palette grouped by category.
Templates tab — 13 starter architectures, labelled by node + edge count.
Inspector — selected node shows engine props, live metrics, chaos buttons, anti-pattern chips.
Microservices fan-out template — gateway routes to two independent service+store pairs in parallel.
Regenerate via bun scripts/screenshots.ts (dev server on :5173).
Architecture deep-dive — hybrid scheduler, determinism, node model, topology JSON, WASM bridge, design decisions.
MIT