Probagraph is a tool for building probability trees and seeing the chance of every outcome. It runs in the browser and as a desktop app on Linux, macOS and Windows.
Web version: https://samherts.github.io/Probagraph/
Desktop app: see Installing for Windows, macOS and Linux.
A tree starts from a single entrance node and grows left to right. Each branch has a probability, and every node shows its chance of being reached: the product of the branch probabilities along its path. The side panel lists every leaf outcome and their total.
Exits are named outcomes, such as "Success" or "Mission lost", that several leaves can lead into. Each exit shows the combined probability of every path that ends in it. Only leaves can lead to an exit, so adding a branch to a linked leaf unlinks it.
Each node shows its chance below its name, and the yellow label on the line into it is the branch probability. Selecting an exit highlights the connections that lead into it.
A leaf can also continue at another node instead of ending, for when different routes lead to the same situation and what happens next is the same either way. The node then merges those routes: its chance is the total of every route into it, it says how many routes lead in, and everything after it is shared, so it only needs building once. Continue links are drawn as dashed arrows. Links that would loop back are refused. Only merge routes when what follows really doesn't depend on how you got there; if it does, keep separate branches.
Simulate runs a single event: starting at the entrance node, it takes each branch at random according to its probability, and highlights the path it took and the exit it reached.
Probabilities can be entered as percentages (25 or 25%) or fractions (1/4). A new branch defaults to whatever probability its siblings haven't used yet. Nodes whose branches don't add up to 100% are outlined in orange. Probabilities are kept to 12 decimal places and shown to 4 (of a percent); a sum that shows as 100% counts as complete.
- Select a node: click it, or move with the arrow keys
- Add a child branch: A or Tab, the toolbar, the right-click menu, or double-click empty space
- Add a sibling branch: S
- Edit a label or probability: double-click the node, Enter, or F2
- Rename an exit or change its color: double-click the exit, Enter, or F2
- Add an exit: X (if a leaf is selected, it is linked to the new exit)
- Link a leaf to an exit: drag the leaf onto the exit, use "Send to exit" in the right-click menu, or pick or type one in the leaf's edit dialog
- Delete a node and its subtree, or an exit: Delete or Backspace
- Continue a leaf at another node: drag the leaf onto the node, or select the leaf, press L (or right-click and choose "Continue at another node…"), then click the node
- Remove a single connection from a leaf to an exit or to the node it continues at: click the connection, then Delete or Backspace
- Split children evenly, or scale them to 100%: toolbar or right-click menu
- Pan: drag empty space, or scroll (Shift for horizontal)
- Zoom: Ctrl+scroll or pinch, Ctrl+plus and Ctrl+minus, Ctrl+0 to reset, F to fit
- Simulate one event: R or the Simulate button. The run starts at the entrance node and takes each branch at random according to its probability, highlighting the path it takes and the exit it reaches. Esc clears it.
- Undo and redo: Ctrl+Z, and Ctrl+Shift+Z or Ctrl+Y (also in the toolbar)
- Save and open: Ctrl+S and Ctrl+O
The web version needs no installing. For the desktop app, download the installer for your system from the latest release: https://github.com/SamHerts/Probagraph/releases/latest
The installers aren't signed with a paid developer certificate, so Windows and macOS warn the first time you open them. The steps below get past that.
Download Probagraph_<version>_x64-setup.exe and run it. If Windows shows "Windows
protected your PC", click "More info", then "Run anyway". The .msi file installs the
same app, for when an MSI package is needed. Windows 10 and 11 already include the
WebView2 runtime the app uses; on older systems the installer downloads it.
Download Probagraph_<version>_universal.dmg, which runs on both Apple Silicon and
Intel Macs. Open it and drag Probagraph into Applications. The first time you open the
app, macOS says it can't verify the developer: click "Done", then open System Settings,
go to Privacy & Security, and click "Open Anyway" next to the message about
Probagraph. After that it opens normally.
There are three packages; use whichever suits your distribution.
On Debian, Ubuntu and similar:
sudo apt install ./Probagraph_<version>_amd64.deb
On Fedora, RHEL and similar:
sudo dnf install ./Probagraph-<version>-1.x86_64.rpm
On any distribution, the AppImage runs without installing:
chmod +x Probagraph_<version>_amd64.AppImage
./Probagraph_<version>_amd64.AppImage
If the AppImage doesn't start, your system may be missing FUSE 2 (sudo apt install libfuse2 on Ubuntu).
Probagraph is written in TypeScript and drawn with SVG. It needs Node.js 20 or newer.
npm install
npm run dev # opens at http://localhost:5173
npm test
npm run build # static site in dist
In the browser, Save writes straight back to the file in Chrome and Edge. Other browsers download a copy instead. The open tree is also kept in the browser's local storage, so refreshing or closing the tab brings it back next time, including unsaved changes. That copy only lives in that browser, so save to a file to keep your work.
The desktop app wraps the same code with Tauri. It needs Rust (https://rustup.rs) and Tauri's system dependencies (https://tauri.app/start/prerequisites/). On Fedora:
sudo dnf install webkit2gtk4.1-devel openssl-devel libappindicator-gtk3-devel librsvg2-devel libxdo-devel dbus-devel
sudo dnf group install c-development
Then:
npm run desktop # run in a window, with live reload
npm run desktop:build # installers in src-tauri/target/release/bundle
Installers can only be built for the system you build on.
Trees are saved as JSON with one node per line. Each node points at its parent's id, so the file stays flat however deep the tree grows:
{
"version": 3,
"exits": ["Win"],
"nodes": [
{"id": 0, "label": "Start"},
{"id": 1, "parent": 0, "label": "A", "prob": 0.25, "exit": "Win"},
{"id": 2, "parent": 0, "label": "B", "prob": 0.75}
]
}A leaf that continues at another node has "next" set to that node's id. An exit with
a chosen color is saved as {"label": "Win", "color": "#16a34a"} instead
of just its name. Files saved in the older nested format still open. examples/mars_lander.json is a
worked example.