Open toolkit for systems modelling


5 Sep 2017
Move to new server.
16 Mar 2015
Preparing for UKSD Annual Meeting, 26-27 March 2015:
Home page for Systo exercises.
13 Mar 2015
Major overhaul, reflecting substantial changes to Systo. Old pages still available at
13 Sept 2013
Systo web site goes live.

Featured web page

Featured model
Glycolysis (biological pathway)

Featured widget
Equation listing A very basic widget - a good starting point for aspiring Systo developers.

Welcome to Systo...

... an open, adaptable and lightweight approach for viewing, building and running systems models in web pages.

A "Hello world" example

Here is the classic predator-prey model, conventionally expressed in terms of "rabbits and foxes".

You can interact with the model diagram in various ways:

  • You can zoom in, zoom out and zoom-to-fit using the buttons on the right of the diagram.
  • You can resize the box the diagram is in, by dragging on the right or bottom edges.
  • You can drag the diagram around, useful if you have a large diagram.
  • You can change the level of detail shown (just stocks and flows; or parameters and influence arrows): just click on the lowest of the 4 buttons (showing 1, 2 or 3).
  • You can even re-arrange the nodes in the diagram (stocks, clouds and variables), by dragging them around! Note that level of detail must be 3 to do this.

You can also explore the dynamic behaviour of the model. Scroll down a bit so you can see the graph below, then move the sliders to change the initial population size of the rabbits and foxes, or the various parameters, and see how:

  • the graphs showing the rabbit and the fox population size; and
  • the inline statistics derived from the simulation results (the maximum for the two populations, and the cycle period)
automatically update as you move the sliders. The computer is continuously re-running the model as you do this! (Yes, it really is that fast.)

The maximum value for the number of foxes is and for the number of rabbits is . The cycle period is years.

You normally only need to do this if a Systo web page fails to load properly, because it is trying to access a corrupted model.

This action will completely clear your Local Storage.

This may affect other web sites you have visited, if they also have cached information in Local Storage.

Are you really sure you want to do this?