(Solved) Which JSON content type do I use?

For JSON text:

application/json

The MIME media type for JSON text is application/json. The default encoding is UTF-8. ^{(Source: RFC 4627)}

For JSONP (runnable JavaScript) with callback:

application/javascript

Here are some blog posts that were mentioned in the relevant comments:

• Why you shouldn’t use text/html for JSON
• Internet Explorer sometimes has issues with application/json
• A rather complete list of Mimetypes and what to use them for
• The official mime type list at IANA from @gnrfan’s answer below