Introduction

What is Symbulator

Symbulator is a program to solve linear electric circuits symbolically and numerically on your device. It takes numerical and symbolic values, and returns numerical and symbolic results. The odd-sounding name is a portmanteau of "symbolic simulator". Symbulator is widely regarded as the best symbolic simulator of linear electric circuits ever made for a handheld device.

What analyses can it do?

Symbulator can solve circuits using four types of analysis: direct current (DC), alternating current (AC), transient time-domain (TR), and complex frequency-domain (FD). It analyses numerical and, more importantly, symbolic linear circuits, returning the voltages in all nodes and the currents, voltage drops and power in all elements. It also finds the passive, Thévenin / Norton and two-port equivalent of a circuit, and draws time domain and Bode plots.

What elements does it accept?

Symbulator accepts elements such as resistors, inductors, mutual inductance, capacitors, independent and dependent current and voltage sources, ideal operational amplifiers, ideal transformers and six types of two-ports.

Where does it run?

Symbulator 9, released in 2026, is a port of the classic code to Python, powered by the SymPy computer algebra library. It runs anywhere Python runs: your mobile phone, tablet, laptop, a Jupyter notebook, or a browser on any computer. Since it is not bound by the memory of a calculator, version 9 solves circuits faster than versions 7 and 8.

Why use Symbulator?

Symbulator is extremely useful on the circuit theory problems engineering students face in Circuits I and II. It lets the student focus on understanding circuit analysis rather than on the mathematics of solving it.

Strengths

• A fantastic tool to solve circuits composed of ideal, linear elements.
• Shines in solving circuits with symbolic values, and symbolic results.
• Offers the absolute simplest way to define dependent sources.
• Includes ideal transformers and six different two-ports.

Limitations

• Does not simulate non-linear elements, such as diodes and transistors.
• Will not answer under-defined problems that rely on applying formulas selectively rather than solving a circuit completely.
• Is not a replacement for your brain or an excuse to not study. You must understand circuit theory to use it.

Symbulator is free!

Symbulator has always been free of cost, and always will be. (You are welcome!)

Since 2026, Symbulator is also open source under the MIT licence. You are free to use it, change it and port it to other platforms; all the licence asks is that the copyright notice and the attribution to the original author travel with it.

Get Symbulator

You can use Symbulator 9 in two ways:

• as an online app running on a remote server, or
• as an offline app running locally on your device.

The easiest way to start is the online app, currently hosted at PythonAnywhere. Click here to go to it.

To install Symbulator 9 as a local app that runs on your device even offline, follow the instructions at the bottom of the online app, under "Run Symbulator 9 locally".

Input files and entries

Everything you put into Symbulator — the circuit, the analysis, the settings, and whatever is in the Evaluate and Solve cards — can be kept and used again. There are two words for it.

• An entry is one set of inputs meant to be solved together: a circuit, the analysis to run on it, and the settings to run it with, along with a name.

• An input file holds as many entries as you like, along with a name, such as Circuits for Lesson 1 of the Tutorial, and that is what you will see it called.

Input files are plain text and require the extension .cir. Using them is optional; the buttons to load, download and create them are in the Input File card at the top of the app.

Loading input files

Symbulator arrives with input files of its own: one for each lesson in this tutorial, holding an entry for every simulation that lesson runs. It is not always one entry per problem — a few problems take more than one simulation, and each gets its own entry — so a lesson file may hold more entries than the lesson has problems. Between them, they let you follow the whole tutorial without typing a circuit at all.

Built-in examples lists the input files available for the lessons; click a title to load it. That link is always there. These files are read-only: load one and change it as much as you like, but you cannot write back to it.

To open an input file of your own, click Upload and choose the .cir file. The dropdown beneath then reads Entries in followed by the file's name. Choosing an entry fills in every box on the page at once — circuit, analysis, settings and all. Then solve it exactly as you would something you had just typed.

Trying to save an entry while a read-only file is loaded, or clicking Create new, starts a new input file of your own, blank by default.

Saving your work

Two links sit under the circuit box, and each appears only when it applies:

• Save inputs to new entry adds what is on screen as a new entry and asks you to name it. This is the one you want the first time.
• Update inputs in this entry writes your changes back into the entry you loaded. It appears once you have actually changed something.

Beside the dropdown, Rename and Delete act on the entry itself. Neither is offered for the built-in examples, since they are read-only.

What an entry remembers

An entry keeps everything you typed, not just the circuit description: the analysis and whatever it needs — the frequency, the two node names for an equivalent, which kind of two-port — the Expert Mode equations, unknowns and conditions, everything in Settings, whatever is in Evaluate and its Conditions, the Solve card, the plot, and a note of your own shown when the entry is loaded.

An entry is not just a circuit: it is everything you give Symbulator to run the analysis. Load one a year later and you are back where you left off, with the same rounding, asking for the same analysis.

The About input file (.cir) format section inside the Input File card explains what input files carry, in detail.

Reading and running side by side

Working through this tutorial means going back and forth between two things: the page you are reading and the app you are running. You can keep them in two windows, and many people do. But there is a tidier way.

The split view puts them side by side in one window: this documentation on the left, the live app on the right. Drag the divider to give whichever side you need more room; on a phone or a narrow window the two become a pair of tabs instead. Everything in either half is the real thing — the same documentation and the same app, simply shown together.

What makes it worth using is that the two halves are connected. On the website, every worked problem in every lesson carries its own pair of links, sitting just under the problem's title:

• Open in app ↗ loads that exact circuit — the description, the analysis, the settings, all of it — ready to run. Read it on the page, then run it yourself without typing a character.

• Open in split view does the same thing, but opens the side-by-side window first, on the very problem you were reading.

Inside the split view, Open in app ↗ loads the circuit into the right-hand pane instead of opening a new tab, so you never leave the page you are reading. The second link disappears there, having nowhere left to take you.

A problem that needs more than one simulation carries a link for each, marked with what that run is: DC for the pass that finds an initial condition, TR for the transient that follows it. A handful of problems have no link at all, because they are worked with pencil and paper rather than by the software. If you are reading this in the PDF, the links are on the web edition at learn.symbulator.com; everything else on this page applies either way.

The split view keeps its address up to date as you move, so the window is always shareable exactly where you are: send someone learn.symbulator.com/split/?lesson=6a&entry=3 and they open on the same problem, with the same circuit loaded beside it.