Can comments be used in JSON?

Question

Can I use comments inside a JSON file? If so, how?

Answer 1

JSON makes a lot of sense for config files and other local usage because it's ubiquitous and because it's much simpler than XML.

If people have strong reasons against having comments in JSON when communicating data (whether valid or not), then possibly JSON could be split into two:

• JSON-COM: JSON on the wire, or rules that apply when communicating JSON data.
• JSON-DOC: JSON document, or JSON in files or locally. Rules that define a valid JSON document.

JSON-DOC will allow comments, and other minor differences might exist such as handling whitespace. Parsers can easily convert from one spec to the other.

With regards to the remark made by Douglas Crockford on this issues (referenced by @Artur Czajka)

Suppose you are using JSON to keep configuration files, which you would like to annotate. Go ahead and insert all the comments you like. Then pipe it through JSMin before handing it to your JSON parser.

We're talking about a generic config file issue (cross language/platform), and he's answering with a JS specific utility!

Sure a JSON specific minify can be implemented in any language, but standardize this so it becomes ubiquitous across parsers in all languages and platforms so people stop wasting their time lacking the feature because they have good use-cases for it, looking the issue up in online forums, and getting people telling them it's a bad idea or suggesting it's easy to implement stripping comments out of text files.

The other issue is interoperability. Suppose you have a library or API or any kind of subsystem which has some config or data files associated with it. And this subsystem is to be accessed from different languages. Then do you go about telling people: by the way don't forget to strip out the comments from the JSON files before passing them to the parser!

Answer 2

Consider using YAML. It's nearly a superset of JSON (virtually all valid JSON is valid YAML) and it allows comments.

Answer 3

Here is what I found in the Google Firebase documentation that allows you to put comments in JSON:

{
  "//": "Some browsers will use this to enable push notifications.",
  "//": "It is the same for all projects, this is not your project's sender ID",
  "gcm_sender_id": "1234567890"
}

Answer 4

JSON is not a framed protocol. It is a language free format. So a comment's format is not defined for JSON.

As many people have suggested, there are some tricks, for example, duplicate keys or a specific key _comment that you can use. It's up to you.

Answer 5

If you are using Jackson as your JSON parser then this is how you enable it to allow comments:

ObjectMapper mapper = new ObjectMapper().configure(Feature.ALLOW_COMMENTS, true);

Then you can have comments like this:

{
  key: "value" // Comment
}

And you can also have comments starting with # by setting:

mapper.configure(Feature.ALLOW_YAML_COMMENTS, true);

But in general (as answered before) the specification does not allow comments.

Answer 6

You can't. At least that's my experience from a quick glance at json.org.

JSON has its syntax visualized on that page. There isn't any note about comments.