json/docs/mkdocs/docs/features/comments.md

Comments

This library does not support comments by default. It does so for three reasons:

1. Comments are not part of the JSON specification. You may argue that // or /* */ are allowed in JavaScript, but JSON is not JavaScript.

2. This was not an oversight: Douglas Crockford wrote on this in May 2012:

   I removed comments from JSON because I saw people were using them to hold parsing directives, a practice which would have destroyed interoperability. I know that the lack of comments makes some people sad, but it shouldn't.

   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.

3. It is dangerous for interoperability if some libraries add comment support while others do not. Please check The Harmful Consequences of the Robustness Principle on this.

However, you can set parameter ignore_comments to #!cpp true in the parse function to ignore // or /* */ comments. Comments will then be treated as whitespace. Combined with ignore_trailing_commas (also a parse parameter), this covers what is commonly referred to as JSONC (JSON with Comments, as used e.g. by Visual Studio Code's .jsonc files) — comments and trailing commas, nothing more. This is a different, smaller extension than JSON5, which additionally allows unquoted keys, single-quoted strings, and other syntax changes that this library does not support.

For more information, see JSON With Commas and Comments (JWCC).

!!! example

Consider the following JSON with comments.

```json
{
    // update in 2006: removed Pluto
    "planets": ["Mercury", "Venus", "Earth", "Mars",
                "Jupiter", "Uranus", "Neptune" /*, "Pluto" */]
}
```

When calling `parse` without additional argument, a parse error exception is thrown. If `ignore_comments` is set to `#!cpp true`, the comments are ignored during parsing:

```cpp
--8<-- "examples/comments.cpp"
```

Output:

```
--8<-- "examples/comments.output"
```

See also

• parse - deserialize from a compatible input
• Trailing Commas - accept trailing commas in arrays and objects
• Parsing - overview of the parsing functions
• Parsing Untrusted Input - limits and checks for input you do not control