Nirai.app
Create interactive system dynamics and stock-and-flow models online. Visualize water flowing through tanks and pipes, run simulations, export MP4 animations.
Create interactive system dynamics and stock-and-flow models online. Visualize water flowing through tanks and pipes, run simulations, export MP4 animations.
This page is designed to help you find out whether Nirai.app is good and if it is the right choice for you.
Nirai is a browser-based system dynamics and stock-and-flow simulator. Unlike traditional tools that show results as line charts, Nirai animates the same model as real water flowing through tanks and pipes — so feedback loops and bottlenecks are something you watch, not decode.
Built on a Rust/WASM engine running entirely client-side — no server round-trips, no install. Sliders update the simulation instantly. Supports RK4 integration, lookup tables, and stochastic functions.
Import existing XMILE files from Vensim or Stella and continue working in Nirai. Export any simulation as a watermark-free MP4 for slides, client decks, or lectures. An AI tutor assists directly on the canvas using your own API key (OpenAI, Gemini, or OpenRouter) — nothing goes through Nirai's servers.
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Stock-and-flow modelling
Build system dynamics models visually with stocks, flows, auxiliaries, and connectors
Interactive visualisation
Simulation renders as real water flowing through tanks and pipes in real time — not line charts
AI tutor
AI assistant proposes and edits stocks and flows directly on your canvas using your own API key
MP4 export
Export the full animated simulation as an MP4 video for slides, decks, or lectures
XMILE import
Import existing models from Vensim or Stella Architect via the XMILE standard
Client-side execution
Rust/WASM engine runs fully in-browser — no server, no install, instant slider feedback
Bring your own API key
Supports OpenAI, Gemini, and OpenRouter — your key stays local, never stored on Nirai servers
Nirai is the only system dynamics simulator that animates your model as real water flowing through tanks and pipes — instead of plotting results as line charts. This makes feedback loops, bottlenecks, and oscillations immediately visible without decoding numbers. It runs entirely in the browser via a Rust/WASM engine with no install required, exports simulations as MP4 videos, imports XMILE files from Vensim and Stella, and includes an AI tutor that edits your model directly on the canvas using your own API key. Nothing is processed on Nirai's servers
Nirai is built with Rust compiled to WebAssembly (WASM) for the simulation engine, using RK4 numerical integration and the fasteval2 formula engine for lookup tables, trigonometric functions, and stochastic expressions. The frontend is Vue 3 with Tailwind CSS, compiled with Vite and pre-rendered as static pages via Vite SSG. The AI assistant integrates with OpenAI, Google Gemini, and OpenRouter via the user's own API key. The app is hosted on Netlify and functions as a Progressive Web App with offline support.
Vensim and Stella Architect require desktop installation, cost hundreds of dollars per year, and show results only as line charts. InsightMaker is browser-based but has no animation, no MP4 export, and no AI assistance. Nirai combines all the things competitors lack: runs in the browser for free, animates the simulation visually, exports MP4 for presentations, imports existing XMILE models so you don't start from scratch, and includes an AI tutor that works on your canvas. Pro is a one-time $99 — not a recurring subscription.
Nirai is built for three groups. Educators and students who teach or learn system dynamics and need a free, browser-based tool that requires no installation and produces shareable, visual results. Analysts and consultants who need to communicate system behaviour to non-technical clients and want to export animated simulations into slides or decks. Engineers and researchers who already use Vensim or Stella and want a faster, browser-native tool that can import their existing XMILE models.
Nirai was built by a solo developer who was frustrated that every system dynamics tool — Vensim, Stella, InsightMaker — shows simulation results as line charts you have to read and interpret. The idea was simple: what if the simulation looked like the thing it was modelling? A supply chain model where you can actually watch inventory surge and lag. An epidemic model where you watch people move between compartments. That visual clarity became the core of Nirai. The simulation engine was built in Rust compiled to WebAssembly so it runs at native speed entirely in the browser, with no server round-trips and no install barrier
Nirai launched in 2026 and is in its early stage. Current users include system dynamics educators, independent analysts, and engineers exploring browser-based alternatives to Vensim and Stella. If you are using Nirai in a classroom or professional context, we'd love to hear from you at admin@nirai.app.
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