demo · v139
+json MIME Explorer
Pick a MIME from the catalogue (or type a custom one) and see how Chrome 138 vs 139 classify it against the WHATWG JSON MIME type rule. The explorer strips parameters, lowercases the essence, handles malformed input, and shows where +json suffixes now become JSON.
your MIME type
| check | Chrome 138 | Chrome 139 |
|---|
Highlighted cells show the old literal allow-list cases that change in Chrome 139. The MIME string itself does not change; Chrome now recognizes the structured +json suffix as a JSON MIME type, matching WHATWG mimesniff.
spec rule
// WHATWG mimesniff §4.6
// A MIME type is a "JSON MIME type" if its essence is:
// application/json
// text/json
// OR its subtype ends with "+json".
function isJSONMimeType(mt) {
return mt.essence === 'application/json'
|| mt.essence === 'text/json'
|| mt.subtype.endsWith('+json');
}