JSON Feed template for Movable Type

json_feed.mtml

{
  "version": "https://jsonfeed.org/version/1",
  "title": "<$mt:BlogName smarty_pants="1" remove_html="1" escape_for_json="1"$>",
  "home_page_url": "<$mt:BlogURL$>",
  "feed_url": "<$mt:BlogURL$>feed.json",
  "description": "<$mt:BlogDescription smarty_pants="1" remove_html="1" escape_for_json="1"$>",
  "favicon": "<$mt:BlogURL$>favicon.ico",
  "items": [
<mt:Entries lastn="5">
    {
      "id": "<$mt:EntryPermalink$>",
      "url": "<$mt:EntryPermalink$>",
      "title": "<$mt:EntryTitle smarty_pants="1" remove_html="1" escape_for_json="1"$>",
      "content_html": "<$mt:EntryBody escape_for_json="1"$>",
      "summary": "<$mt:EntryExcerpt escape_for_json="1"$>",
      "date_published": "<$mt:EntryDate utc="1" format_name="iso8601"$>",
      "date_modified": "<$mt:EntryModifiedDate utc="1" format_name="iso8601"$>",
      "author": {
        "name": "<$mt:EntryAuthorDisplayName escape_for_json="1"$>"
      }
    }<mt:Unless name="__last__">,</mt:Unless>
</mt:Entries>
  ]
}

I note that your template doesn't have an entry for tags (aka categories). I think the following works:

      <mt:if tag="EntryCategory">"tags": [<mt:EntryCategories glue=", ">"<$mt:CategoryLabel escape_for_json="1"$>"</mt:EntryCategories><mt:if tag="Tags">, <mt:EntryTags glue=", ">"<$mt:TagName escape_for_json="1"$>"</mt:EntryTags></mt:if>],
      <mt:ElseIf tag="Tags">"tags": [<mt:EntryTags glue=", ">"<$mt:TagName escape_for_json="1"$>"</mt:EntryTags>],</mt:if>

JSONfeed doesn't distinguish between tags and categories, so I've combined them. However, because of (I think) the lack of boolean "or", I split this into two parts, one of there are Categories and possibly tags, and another if there are only tags.