JSON MIME Type

About JSON files

JSON is always UTF-8 (RFC 8259), so the type has no charset parameter: application/json alone is correct, and ; charset=utf-8 is harmless but ignored. text/json and application/x-json are old unofficial names. Types like application/problem+json and application/geo+json are JSON too; the +json suffix tells generic tools they can parse them.

• If fetch(…).then(r => r.json()) fails with “Unexpected token <”, the server sent HTML (usually an error or login page) instead of JSON. Check the status code and the Content-Type before parsing.
• For a JSON API, also send X-Content-Type-Options: nosniff, so a browser never treats a response as HTML.

Other types seen for these files: text/json , application/x-json . Accept them when reading uploads, but send application/json yourself.

File signature

JSON has no fixed signature: it is data without a magic number, so validate uploads by parsing the content rather than by checking bytes.

Serve .json with the right Content-Type

Content-Type: application/json

application/json json map;

AddType application/json .json .map

@json path *.json *.map
header @json Content-Type "application/json"

curl -sI https://example.com/file.json | grep -i '^content-type'
# Content-Type: application/json

Set the type in code

res.set('Content-Type', 'application/json');
// Or make the browser download it:
res.attachment('file.json');

import mimetypes

mimetypes.add_type('application/json', '.json')  # if your system doesn't know it
mimetypes.guess_type('file.json')[0]  # 'application/json'

mime.AddExtensionType(".json", "application/json")
w.Header().Set("Content-Type", "application/json")

Accept .json uploads

<input type="file" accept=".json,.map,application/json">

The accept attribute only filters the file picker; users can still choose another file. Listing the extension as well as the type matters, because operating systems don’t always report the type you expect.

Related types

• .ndjson (application/x-ndjson): JSON Lines (NDJSON)
• .jsonld (application/ld+json): JSON-LD
• .geojson (application/geo+json): GeoJSON
• .xml (application/xml): XML

More data and text

.txt , .csv , .tsv , .md , .yaml , .ics , .sql . Look up any extension or type with the MIME type lookup.

Sources

• IANA registration: application/json
• MDN: Common media types

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Frequently asked questions