You'd have to escape the special characters, but the method should be the same. Example:
when HTTP_REQUEST {
set json "{ \"glossary\": { \"title\": \"example glossary\", \"GlossDiv\": { \"title\": \"S\", \"GlossList\": { \"GlossEntry\": { \"ID\": \"SGML\", \"SortAs\": \"SGML\", \"GlossTerm\": \"Standard Generalized Markup Language\", \"Acronym\": \"SGML\", \"Abbrev\": \"ISO 8879:1986\", \"GlossDef\": { \"para\": \"A meta-markup language, used to create markup languages such as DocBook.\", \"GlossSeeAlso\": \[\"GML\", \"XML\"\] }, \"GlossSee\": \"markup\" } } } } }"
HTTP::respond 200 content $json "Content-Type" "application/json"
}