Distributed architecture simulation & interview prep
SysSimulator is a free browser architecture simulator: sketch distributed topologies, run discrete-event traffic in WebAssembly, inject chaos, and read rough AWS cost bands—no account. Open the simulator to stress bottlenecks and practice failure narratives for interviews and learning.
Open the simulator →Software engineers, students, and bootcamp grads preparing for system design interviews; tech leads explaining tradeoffs to a team; and anyone learning chaos engineering or microservices behavior without spinning up a cloud lab.
It is a fast way to visualize request flow, failure modes, and cost direction on a diagram you control.
It isn’t wired to your real AWS account, doesn’t observe live production traffic, and doesn’t certify availability — use it to build intuition and talking points.
Distributed system simulation lets you model how real infrastructure behaves under traffic load, component failure, and extreme conditions — before you build it. Instead of discovering bottlenecks in production, you can test them in a safe sandbox.
SysSimulator uses a Discrete Event Simulation (DES) engine written in Rust, compiled to WebAssembly, running entirely in your browser. Requests are modeled as events that flow through your topology — through load balancers, app servers, caches, and databases — respecting real latency distributions, concurrency limits, and failure modes.
Design your architecture on an infinite canvas. Drag components from the palette, connect them with bezier wires, and configure each node's behavior — throughput, latency, connection limits, and more.
Run your simulation at 10–100,000 RPS with configurable speed multipliers. Colored particles flow along wires: green (success), yellow (degraded), red (failed). Per-component metrics update in real-time.
Test your architecture's resilience by injecting real-world failure modes and observing cascade effects. Scenarios roll up into six themes; a seventh, MCP-only set (tool timeouts, token budget pressure, policy denials, vector index staleness, and more) unlocks automatically on MCP / AI agent blueprints.
Every component maps to real AWS pricing. As you design and adjust traffic, the cost estimator updates live — broken down by Compute, Storage, Networking, and Requests.
| Feature | SysSimulator | Lucidchart | draw.io | Excalidraw |
|---|---|---|---|---|
| Real-time traffic simulation | ✓ | ✗ | ✗ | ✗ |
| Chaos engineering | ✓ | ✗ | ✗ | ✗ |
| AWS cost estimation | ✓ | ✗ | ✗ | ✗ |
| Runs in browser (no install) | ✓ | ✓ | ✓ | ✓ |
| Free to use | ✓ Free | Freemium | ✓ Free | ✓ Free |
| Pre-built architecture blueprints | ✓ 57 | Limited | ✗ | ✗ |
| Per-component latency metrics | ✓ | ✗ | ✗ | ✗ |
| No sign-up required | ✓ | ✗ | ✓ | ✓ |
SysSimulator is a free browser-based tool to visually design distributed system architectures, simulate real-time traffic, inject chaos scenarios, and estimate AWS costs — no installation, no sign-up. Diagrams are stored locally in your browser (localStorage) unless you export JSON/PNG, create a share link (which may store a time-limited copy on the host), or submit optional feedback.
Yes, completely free. No accounts, no payment, no rate limits. The simulation engine runs in your browser via WebAssembly.
The simulation engine is written in Rust and compiled to WebAssembly. It uses Discrete Event Simulation (DES) to model request flows, processing latencies, failure modes, and real-time metrics across your topology.
Absolutely. Load one of the 57 pre-built blueprints (E-Commerce, Chat, Serverless API, Payment System, Stock Exchange, ML Pipeline, MCP agents, and more) to explore common patterns. Run traffic to see bottlenecks and inject chaos to practice failure storytelling — typical interview depth.
Diagrams auto-save to your browser's localStorage. Use Export as JSON or Export as PNG for files you keep forever. Copy share link uploads your diagram JSON to a serverless API and returns a short URL; the copy is kept about 7 days, then expires. For archives and full control, prefer JSON export.
28 chaos scenarios across six themes: Network (latency, partition, packet loss, bandwidth throttle), Infrastructure (node failure, disk, CPU, memory pressure), Traffic (spikes, slow clients, thundering herd), Data Layer (database, replication, cache, pools), Application (leaks, threads, deadlock, cascade), and Dependency (timeouts, errors, rate limits). Additional MCP-only scenarios (tool servers, token budgets, vector indexes) appear when you load MCP or agent blueprints.
SysSimulator runs in your browser — no installation, no account. Just open it and start designing.
Launch the Simulator →