WebSpice

A browser-based SPICE circuit simulator with a minimal GUI. Runs entirely client-side using NGSpice compiled to WebAssembly.

Features

• Schematic Editor: Canvas-based editor with component placement, wire routing, and grid snapping
• Component Library: Resistor, Capacitor, Inductor, Voltage Source, Current Source, Ground, Diode, BJT (NPN/PNP), MOSFET (NMOS/PMOS)
• Netlist Generation: Automatic SPICE netlist generation from schematic
• Simulation: Transient analysis via NGSpice WASM (runs in Web Worker)
• Waveform Viewer: WebGL-based plotting with pan, zoom, cursors, and multiple tabs
• Probing: Voltage probes (click on wire), current probes (click on component), differential voltage (drag between nodes)
• Persistence: Save/load schematics as JSON files

Keyboard Shortcuts

Key	Function
R, C, L, V, I, G, D, Q, M	Place component
W or 3	Wire mode
5	Delete mode
6	Duplicate mode
7	Move mode
P	Probe mode
Ctrl+R	Rotate selected
Ctrl+E	Mirror selected
Ctrl+N	Generate netlist
Ctrl+B	Run simulation
Ctrl+S	Save schematic
Ctrl+O	Open schematic
Escape	Cancel operation

Tech Stack

• Framework: SvelteKit 2 + Svelte 5
• Build: Vite
• Language: TypeScript
• Simulation: eecircuit (NGSpice WASM)
• Editor: CodeMirror 6 (SPICE syntax highlighting)
• Plotting: webgl-plot
• Web Workers: Comlink

Development

# Install dependencies
pnpm install

# Start development server
pnpm dev

# Build for production
pnpm build

# Preview production build
pnpm preview

Project Structure

src/
  lib/
    components/     # UI components (ResizablePanel)
    editor/         # CodeMirror netlist editor
    netlist/        # Connectivity analysis, netlist generation, current calculation
    schematic/      # Canvas editor, component definitions, renderer
    simulation/     # NGSpice WASM wrapper, Web Worker
    waveform/       # WebGL waveform viewer
  routes/
    +page.svelte    # Main application

Acknowledgments

• LTSpice by Analog Devices - Inspiration for UI design and keyboard shortcuts
• NGSpice - Open source SPICE simulator
• EEcircuit - Demonstrated NGSpice WASM feasibility; eecircuit-engine provides the simulation backend

License

MIT