Engines

SpiceBook supports two SPICE simulation engines. Each notebook is bound to one engine, selected when you create it (or changed later via the toolbar).

ngspice

The default engine. ngspice is an open-source circuit simulator that runs natively on the SpiceBook backend — no additional setup required.

Strengths:

• Always available — built into the backend container
• Broad analysis support: .op, .dc, .tran, .ac, .noise, .pz
• Well-documented netlist syntax with extensive model libraries
• Fast for small-to-medium circuits

Typical use: General-purpose simulation, educational circuits, quick prototyping.

LTspice

Available when the SpiceBook backend is configured with mcltspice, an MCP server that automates LTspice via Wine on Linux.

Strengths:

• Proprietary solver with strong convergence for switching circuits
• Extensive built-in component library (power semiconductors, op-amps, regulators)
• Better performance on large circuits with many timesteps
• Tight .meas directive support for automated measurements

Typical use: Power electronics, switching regulators, circuits using manufacturer models.

Caution

LTspice availability depends on the server configuration. If mcltspice isn’t running, selecting “ltspice” as the engine will return an error when you try to simulate. The engine selector in the toolbar shows which engines are available.

Differences That Matter

Feature	ngspice	LTspice
Availability	Always	Requires mcltspice
Operating point (.op)	Yes	Yes
Transient (.tran)	Yes	Yes
AC sweep (.ac)	Yes	Yes
Convergence on switchers	Fair	Excellent
Built-in device models	Community libs	Extensive vendor libs
Output format	Raw binary	Raw binary

Both engines produce the same WaveformData structure in SpiceBook — the waveform viewer, SVG plots, and schematic generation work identically regardless of which engine ran the simulation.

Choosing an Engine

For most circuits, ngspice works well and requires no configuration. Reach for LTspice when you need:

• A specific manufacturer model that ships with LTspice (LT1234, LTC3780, etc.)
• Better convergence on circuits with fast switching edges
• .meas directives for automated waveform measurements

You can switch engines on an existing notebook at any time — the netlist syntax is largely compatible. Re-run cells after switching to regenerate results with the new engine.