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Cataclysm: Bright Nights

JSON Style Guide

Like in C++ Code Style, 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.

Why do we have a homegrown JSON formatter?

DDA wrote their own JSON parser. It lives in tools/format/format.cpp and it leverages src/json.cppto parse and emit JSON.

This isn’t optimal solution as it makes using existing JSON formatters (e.g deno fmt) impossible, but last attempt proved that the disadvantages outweighed possible benefits.

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 invoked via the Makefile, directly as tools/format/json_formatter.cgi (built via make style-json), or via cgi at

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. 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.

For Single file

To style one JSON file you can run json_formatter.exe path/to/file.json. This will style that one file. If it prints “needs linting”, the file wasn’t styled, but now should be. You can use drag&drop: drag the json file onto the json_formatter icon, then wait a few seconds.

On *nix

Run make style-json in main repo directory.