The sort-package-json package sorts not only dependencies and devDependencies, but other keys as well. I know the original questions didn't ask about the other keys, but I think it's cool to have all keys sorted.

You can simply run:

npx sort-package-json

Example from the package page:

$ cd my-project

$ cat package.json
{
  "dependencies": {
    "sort-package-json": "1.0.0",
    "sort-object-keys": "1.0.0"
  },
  "version": "1.0.0",
  "name": "my-awesome-project"
}
 
$ npx sort-package-json
package.json is sorted!
 
$ cat package.json
{
  "name": "my-awesome-project",
  "version": "1.0.0",
  "dependencies": {
    "sort-object-keys": "1.0.0",
    "sort-package-json": "1.0.0"
  }
}

This does not remove the trailing newline like the npm-sort package mentioned by Wolfgang.

Multiple files

$ sort-package-json "my-package/package.json" "other-package/package.json"

$ sort-package-json "package.json" "packages/*/package.json"

OK, I've found a halfway decent way to integrate without hacking.

1. First remove the general setting "auto-sort" from your settings.json to ensure that it does not apply globally to all files. Here's what you should remove:

"editor.codeActionsOnSave": {
    "source.sort.json": "always"
}

2. Next, reapply the setting specifically for JSON files (set Prettier as the default formatter):

"[json]": {
  "editor.codeActionsOnSave": {
    "source.sort.json": "always"
  },
  "editor.defaultFormatter": "esbenp.prettier-vscode"
},

3. Classify package.json as jsonc (JSON with comments), which is not targeted by the auto-sort setting. Add this to your settings.json:

"files.associations": {
  "package.json": "jsonc"
}

4. Finally, set the default formatter for JSONC files, and deactivate auto-sort:

"[jsonc]": {
  "editor.codeActionsOnSave": {
    "source.sort.json": "never"
  },
  "editor.defaultFormatter": "esbenp.prettier-vscode"
},

Until a more convenient solution is implemented by the VSCode developers, you can use this solution here.

Every JSON will be sorted and every JSONC not. You can extend this list below:

"files.associations": {
  "package.json": "jsonc", 
  "settings.json": "json"
}

With this setup, package.json remains untouched by the auto-sort feature, while files like settings.json continue to be sorted. This distinction hinges on the file extension — json for sorting, jsonc for no sorting.

Be aware of the last letter c

Another Example

  "files.associations": {
    "de.json": "json",  // sort
    "en.json": "json",  // sort
    "fr.json": "json",  // sort
    "nx.json": "jsonc", // do not sort
    "package.json": "jsonc", // do not sort
    "project.json": "jsonc", // do not sort
    "settings.json": "json", // sort
    "tsconfig.app.json": "jsonc", // do not sort
    "tsconfig.base.json": "jsonc", // do not sort
    "tsconfig.e2e.json": "jsonc", // do not sort
    "tsconfig.editor.json": "jsonc", // do not sort
    "tsconfig.json": "jsonc", // do not sort
    "tsconfig.lib.json": "jsonc", // do not sort
    "tsconfig.spec.json": "jsonc" // do not sort
  },