NDJSON MIME Type

About JSON Lines (NDJSON) files

One JSON value per line, so files can be streamed, appended to and split without parsing the whole thing. There is no registered type; application/x-ndjson is the most common (Elasticsearch’s bulk API requires it), and application/jsonl is also seen. Responses are often streamed with it, one event per line.

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

File signature

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

Serve .ndjson with the right Content-Type

Content-Type: application/x-ndjson

application/x-ndjson ndjson jsonl;

AddType application/x-ndjson .ndjson .jsonl

@ndjson path *.ndjson *.jsonl
header @ndjson Content-Type "application/x-ndjson"

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

Set the type in code

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

import mimetypes

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

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

Accept .ndjson uploads

<input type="file" accept=".ndjson,.jsonl,application/x-ndjson">

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

• .json (application/json): JSON
• .csv (text/csv): CSV
• .txt (text/plain): Plain text

More data and text

.tsv , .md , .jsonld , .xml , .yaml , .geojson , .ics , .sql . Look up any extension or type with the MIME type lookup.

Sources

• IANA Media Types registry (not listed)
• MDN: Common media types

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Frequently asked questions