What JSON formatter does Visual Studio Code use to format JSON?

Visual Studio Code has built-in JSON tools, including a formatter: https://code.visualstudio.com/docs/languages/json#_formatting

1. What underlying JSON formatter does Visual Studio Code use?
2. Is it available to use as a command line tool outside of Visual Studio Code?
3. How does it differ from jq?

Here's how to find the info you're looking for

• Find the source code for the extension you're interested in. In this case, it's a builtin VS Code extension, so see https://github.com/microsoft/vscode/tree/main/extensions. There, you'll see the json-language-features subdirectory.
• Open https://github.dev/microsoft/vscode
• Open the Search view and expand the Search Details
  • In "File to include", put "extensions/json-language-features/**/*.ts".
  • Enable regex mode and in the search field, put \bformat\b.
• Learn that in jsonServer.ts, there's an onFormat function that makes a call to languageService.format, where languageService comes from getLanguageService, which comes from the vscode-json-languageservice package.
• Look at microsoft/vscode-json-languageservice/jsonLanguageService.ts and learn that getLanguageService returns an object containing format: (document: TextDocument, range: Range, options: FormattingOptions) => format(document, options, range),, where format comes from import { format } from './utils/format';.
• Look at microsoft/vscode-json-languageservice/utils/format.ts and learn that format calls formatJSON, where that comes from import { format as formatJSON, Range as JSONCRange } from 'jsonc-parser';.
• Look at microsoft/vscode-json-languageservice/package.json's "dependencies" field, and see that it depends on the jsonc-parser package.

So to answer your questions:

> 1. What underlying JSON formatter does Visual Studio Code use?

https://www.npmjs.com/package/jsonc-parser

> 2. Is it available to use as a command line tool outside of Visual Studio Code?

Yes. Use it in the same way that microsoft/vscode-json-languageservice uses it. Add it as a dependency of a JS project in the same way you'd depend on any other NPM package.

> 3. How does it differ from jq? https://stedolan.github.io/jq/

Well, for one thing, it supports JSON with comments, which jq doesn't (see https://github.com/stedolan/jq/wiki/FAQ#processing-not-quite-valid-json and https://stackoverflow.com/q/33352930/11107541).