ngspice

Overview

ngspice is an open-source SPICE simulator for electric and electronic circuits, aimed at users who describe designs in netlists and files instead of drawing them. It suits engineers, educators, developers, and technically confident hobbyists who need analog, digital, or mixed-signal analysis without a license fee. Its broad model and integration support is the main reason to choose it; the absence of schematic entry is the key reason to choose something else.

Key features

The simulator handles analog, digital, and mixed-signal circuits represented as netlists. Its device coverage includes active, passive, analog, and digital elements, and it can use model parameters from collections, manufacturers, and foundries. Compatibility with PSPICE and LTSPICE device-model parameters and discrete-circuit netlists is valuable when a team already has SPICE files or established model libraries. It reduces the need to rebuild existing inputs, but still requires users to understand and maintain those textual descriptions.

Mixed-signal work can combine Verilog blocks compiled with Verilator and, since ngspice-44, VHDL blocks through GHDL. The OSDI/OpenVAF interface adds Verilog-A compact device models without requiring programming on the ngspice side. Those facilities make ngspice relevant to workflows that cross hardware-description and compact-model formats, although they do not turn it into a visual schematic editor.

For software developers, ngspice can be compiled as a shared library or DLL and controlled by a calling application. Listed integrations include KiCad, Autodesk Fusion, and Python interfaces such as PySpice. These options let ngspice serve as a simulation engine inside a broader design or automation workflow rather than only as a standalone command-line program.

The decisive limitation is input. There is no schematic capture: circuits are entered through command-line or file-based methods. That is efficient for reproducible, scriptable work and awkward for anyone who expects to place symbols and wire a circuit inside the simulator.

Pricing

ngspice has one free plan at free, billed Free. It includes the circuit simulator with command-line or file-based input and explicitly provides no schematic entry. There are no paid tiers, seat charges, quotas, or renewal terms stated for this plan, so it is a straightforward fit for individuals, classrooms, and teams that can work within a netlist-first process.

Platforms

ngspice supports Linux, macOS, self-hosted deployments, and Windows. The stable download page provides source archives and Windows binaries. Linux users are directed to their distributor or to compiling from source, while the project's own macOS release is currently unavailable on that page. Support resources include mailing lists, discussion forums, a bug tracker, an FAQ, and documentation.

Who it's for

Choose ngspice if you need advanced electrical simulation, SPICE-compatible models, or mixed-signal co-simulation and are comfortable editing netlists or integrating a simulation library into another application. It is particularly suitable when PSPICE or LTSPICE materials, Verilog, VHDL, or Verilog-A models already belong to the workflow. Look elsewhere if schematic capture is a requirement, if circuit entry must be graphical, or if your users are not prepared to manage command-line and file-based inputs.

Pros and cons

• Pro: Free and open source, with no paid tier standing between a user and the simulator.
• Pro: Analog, digital, and mixed-signal simulation plus active, passive, and logic device models cover varied circuit-analysis needs.
• Pro: PSPICE and LTSPICE parameter and netlist compatibility can preserve existing discrete-circuit work.
• Pro: Verilator, GHDL, OSDI/OpenVAF, shared-library, and DLL options support advanced integration and automation.
• Con: No schematic entry means every design must be supplied through command-line or file-based input.
• Con: Linux installation may require a distributor package or source compilation, and the project's own macOS release is not provided on the stable download page.

Alternatives

For broader physics simulation, OpenFOAM is a free, open-source option on Linux, macOS, self-hosted, and Windows; choose it when fluid and general computational-physics work matters more than SPICE circuit analysis.

OpenSim is another free, open-source platform for API, Linux, macOS, and Windows, with downloads requiring a SimTK account; it is the better direction when its platform focus matches your project instead of electrical netlists.

SimFlow offers a free tier and free trial across Linux, macOS, web, and Windows; choose it when you want a freemium, cross-platform simulation product rather than ngspice's command-line-first model.

Xcos is freely distributed with Scilab on Linux, macOS, and Windows, making it a reasonable choice when a Scilab-based environment is preferable.

Open Source Physics is free across Android, iOS, Linux, macOS, web, and Windows; pick it when broad device access is more important than ngspice's SPICE compatibility.

FeenoX is free, GPLv3+, and targets GNU/Linux without a graphical interface; it suits users seeking an API-oriented open-source solver rather than an electrical SPICE engine.

COMSOL Multiphysics is a paid product with a free trial and broad desktop, web, API, and self-hosted platform coverage; choose it when a commercial multiphysics environment and quotation-based licensing fit the project.

GNU FisicaLab is free software under GNU GPL version 3 or later for Linux and Windows, and is an alternative for users whose needs align with that application.

Verdict

ngspice is the right choice for technically confident users who want a free, SPICE-compatible engine with strong model reuse, mixed-signal support, and application-integration options. Its netlist-first workflow is also its defining constraint: choose another tool if drawing schematics inside the simulator is central to your work.