How do I simulate a circuit in the browser with ngspice?

Last checked 2026-11-11 against the live tool page.

Short answer

Circuit Lab is a free browser workbench. It has a schematic editor, an ngspice simulator compiled to WebAssembly, a waveform viewer and a simple PCB view. No install is needed, and projects stay in your browser.

Steps

Open the workbench and place parts from the component library: resistors, capacitors, voltage sources, ground.
Wire the parts in the schematic. Edit values in the Inspector.
Press Run simulation. Supported analyses are transient, AC and DC operating point.
Read the result in the waveform viewer. Use cursors to read values, toggle legend entries, or export CSV.
Optional: switch to PCB view to place footprints on an 80 x 50 mm board.

Limits to know

Component models are generic. Check real parts before you order.
The PCB view does not change schematic connections.
Schematic-to-PCB sync works for basic components only.
The animated CircuitJS view is for visualization. Use the ngspice waveforms for exact values.
JavaScript must be enabled.

Export

You can export a KiCad project and the SPICE netlist from the Export menu.

BOM checker for checking the parts list before assembly.