ngspice

ngspice is a free, open-source circuit simulator built for working from netlists and device models. It suits engineers, students, and developers who are comfortable with command-line or file-based input. Its SPICE compatibility and mixed-signal support make it capable, while the lack of schematic entry narrows its appeal.

Overview

ngspice simulates electric and electronic circuits across analog, digital, and mixed-signal designs. Its support for PSPICE and LTSPICE parameters and netlists for discrete circuits can help users carry existing SPICE materials into a simulation workflow. The trade-off is fundamental: circuits must be supplied through commands or files, so users who want to draw a schematic as their starting point will need another tool for that part of the work.

Key features

The simulator includes models for active and passive components as well as analog and digital elements. It can draw on model parameters from collections, manufacturers, and foundries, giving users working with established device models a broad basis for describing circuits.

Mixed-signal co-simulation supports Verilog blocks compiled with Verilator and VHDL blocks using GHDL since ngspice-44. The OSDI/OpenVAF interface integrates Verilog-A compact device models without requiring programming on the ngspice side. These capabilities suit designs that combine circuit simulation with hardware-description-language blocks or compact device models.

For developers, ngspice can be compiled as a shared library or DLL and controlled by a calling application. The project also lists integrations with KiCad, Autodesk Fusion, and Python interfaces including PySpice. This creates options for incorporating simulation into a broader software workflow, though the simulator itself still takes command-line or file-based input.

Pricing

The ngspice plan is free: free, billed Free. It includes the circuit simulator, command-line or file-based input, advanced electrical simulation, and standards libraries. There is no paid tier or seat-based price to weigh, but the free plan also has no schematic entry. Users who need a visual circuit editor should account for that workflow gap when considering the zero cost.

Platforms

ngspice supports Linux, macOS, Windows, and self-hosted deployment. The stable download page provides source archives and Windows binaries. Linux users are directed to their distributor or to compile from source, while the project's own macOS release is currently unavailable there; macOS users should check their distribution route before settling on it.

Who it's for

ngspice is a strong fit for circuit designers and learners who already describe circuits as netlists, need compatibility with PSPICE or LTSPICE material, or work with analog, digital, and mixed-signal models. Developers can also use its shared-library or DLL form under the control of another application. It is a weaker choice for anyone who depends on schematic capture as part of circuit creation.

Support resources include mailing lists, discussion forums, a bug tracker, an FAQ, and documentation. That gives users several project channels for getting help and finding guidance around a tool whose input workflow assumes technical familiarity.

Pros and cons

Pros

• Free plan includes advanced electrical simulation and standards libraries, with no paid tier required.
• PSPICE and LTSPICE compatibility can accommodate existing discrete-circuit netlists and device-model parameters.
• Verilator, GHDL, and OSDI/OpenVAF support extend simulation across mixed-signal blocks and Verilog-A compact models.
• Shared-library and DLL builds allow control by a calling application.

Cons

• No schematic entry; users must provide command-line input or files.
• Linux users need a distributor package or source compilation, and the project's stable download page currently has no macOS release.

Alternatives

For other free physics simulation options, see Physics Simulation Software. For software focused on electrical design, browse Electrical Design Software.

• OpenFOAM is another free, open-source option if you want a physics simulator whose support and code customisation are separate services.
• OpenSim is a free, open-source platform to consider if its platform availability suits your setup; downloading it requires a SimTK account.
• Xcos is free and distributed with Scilab, a fit if you prefer software packaged with that environment.
• SimFlow offers a free plan and a free trial across Linux, macOS, web, and Windows; consider it if you want a web option as well.
• GNU FisicaLab is free software under GNU GPL version 3 or later and supports Linux and Windows.
• FeenoX is a free option for users who want a tool with API and web platforms; it has no graphical interface and targets GNU/Linux.
• Step is a free option for Linux users.
• ASCEND is free, open-source software available for Linux, macOS, and Windows.

Verdict

Choose ngspice if you want a free circuit simulator with SPICE-compatible inputs, extensive model support, and mixed-signal integration, and you are prepared to work from netlists or files. The main reason to look elsewhere is the absence of schematic entry; it is not an all-in-one visual circuit-design workspace.