JSON Style Guide

Like in CODE_STYLE.md, the JSON styling policy is to update JSON as it is added or edited, and in relatively small chunks otherwise in order to prevent undue disruption to development.

We haven’t been able to find a decent JSON styling tool, so we wrote our own. It lives in tools/format/format.cpp and it leverages src/json.cpp to parse and emit JSON. json_formatter.cgi can be found in any released build and is already compiled, see Formatting tool.

JSON Example

This example outlines most of the styling features:

    "type": "foo",
    "id": "example",
    "short_array": [ 1, 2, 3, 4, 5 ],
    "short_object": {
      "item_a": "a",
      "item_b": "b"
    "long_array": [
      "a really long string to illustrate line wrapping, ",
      "which occurs if the line is longer than 120 characters"
    "nested_array": [
        [ "item1", "value1" ],
        [ "item2", "value2" ],
        [ "item3", "value3" ],
        [ "item4", "value4" ],
        [ "item5", "value5" ],
        [ "item6", "value6" ]

Indention is two spaces. All JSON delimiters except comma and colon are surrounded by whitespace (either a space or a newline). Comma and colon are followed by whitespace. Object entries are always newline-separated. Array entries are newline-separated if the resulting array would exceed 120 characters otherwise (including indention). Line breaks occur after open brackets, close brackets, or entries.

Formatting tool

The formatting tool can be found alongside the releases as json_formatter.exe or json_formatter.cgi, built via make style-json, or accessed at http://dev.narc.ro/cataclysm/format.html. It is recommended to add the formatting tool’s location to your PATH or (if not already present) put it in your Cataclysm-DDA root directory.

Using make style-json will format all files included in the JSON validation test, alternatively:

# Using git to filter JSON files with uncommitted changes (provided there are no spaces in the file or directory names).
git diff --name-only '*.json' | xargs -P 0 -L 1 json_formatter

# Using git to filter modified JSON files in the current branch.
git diff master --name-only '*.json' | xargs -P 0 -L 1 json_formatter

# Per-folder formatting.
find path/to/desired/folder -name "*.json" -print0 | xargs -P 0 -0 -L 1 json_formatter

If you’re using the Visual Studio solution, you can configure Visual Studio with commands to format all of the JSON in the project.

  1. Build the JsonFormatter project by either building the entire solution or just that project. This will create a tools/format/json_formatter.exe binary.
  2. To automatically lint json you need to define an MSBuild variable ( this is similar to setting up ccache in Visual Studio compiling doc ). If done correctly then trying to build or run the solution will trigger linter and the Output and Error List windows will show the linted files if any. One of the easier methods to do so is creating a Directory.Build.props file in the root of cataclysm project repository with the following contents: ```xml


  1. To add an entry to manually run the json linter tool; Add a new external tool entry ( Tools > External Tools.. > Add ) and configure it as follows:
    • Title: Lint All JSON
    • Command: C:\windows\system32\windowspowershell\v1.0\powershell.exe
    • Arguments: -file $(SolutionDir)\style-json.ps1
    • Initial Directory: $(SolutionDir)
    • Use Output window: checked

At this point, you can use the menu ( Tools > Lint All JSON ) to invoke the command and can look in the Output Window for the output of running it. Additionally, you can configure a keybinding for this command by navigating to Tools > Options > Environment > Keyboard, searching for commands containing Tools.ExternalCommand and pick the one that corresponds to the position of your command in the list (e.g. Tools.ExternalCommand1 if it’s the top item in the list) and then assign shortcut keys to it.

Visual Studio Code

If you install the recommended extensions you should have access to the the cdda-toys.cdda-json-formatter which will auto format your json.