You have seen so many purported “standards” for the JSON content type:
application/jsonapplication/x-javascripttext/javascripttext/x-javascripttext/x-json
But which is correct, or best?
In this article will discuss which one we should use:
For JSON text:
The MIME media type for JSON text is application/json. The default encoding is UTF-8. (Source: RFC 4627).
IANA has registered the official MIME Type for JSON as application/json.
When asked about why not text/json, Crockford seems to have said JSON is not really JavaScript nor text and also IANA was more likely to hand out application/* than text/*.
For JSON:
Content-Type: application/json
For JSON-P:
Content-Type: application/javascript
Here are some blog posts that were mentioned in the comments that are relevant