A .json file gets one of two backends: text, which you can edit, or the tree viewer, which you can only look at. Which one it gets is the file's role, not its extension.

project.json open as text, in the Editor panel

the same file as a tree: nodes, the node count, and Pretty Print

Why two backends

A project's own configuration is JSON and would go to the viewer by extension, and the viewer draws a tree and has nothing to type into. Those are the files the user is told to edit by hand — exports.json holds the PROGRAM order, a task file its cycle time — so they open as text.

Every other .json gets the tree.

Outside a project there are no configuration files, so a .json there is a tree.

Switching

Right-click any .json in the Workspace tree:

Open as Text
Open as Tree

Both replace the tab rather than adding a second one. One file is one row in the tab bar, and the row is whichever view it is in.

The tree viewer

Read-only, and it says so rather than pretending otherwise.


Expand All / Collapse All	open or close every node
Search	keep only the nodes whose key or value matches
Pretty Print	the file re-serialised with two-space indentation, instead of the tree
Hover a value	its full text as a tooltip, so a long value can be read
Header	the file name and the number of nodes

There is no Open File button in the viewer. Files are opened from the Workspace tree, and EditorApp::openFile is what puts one in a tab.

The configuration files

All JSON, no TOML, and nothing reads or migrates the old format:

File	What it holds
`.undoProject/project.json`	the project's name, version, author and creation date; the target architecture, OS and kernel; and the semantics settings
`.undoProject/plcs.json`	the PLCs in the project
`.undoProject/tasks.json`	the task list
`undoCore/tasks/<name>.json`	one task: its PLC, cycle, priority and CPU
`undoLogic/<plc>/exports.json`	the PROGRAM order of one PLC

strictness under semantics is a boolean rather than the "on" / "off" string it was before, and a project written before that key existed reads as strict, which is what a new project is written with.