.ndjson MIME type

application/x-ndjson. You may also see application/jsonl, but application/x-ndjson is the one to send. The same type covers .jsonl.

Content-Type: application/x-ndjson. It compresses well, so let the server apply gzip or Brotli.

Newline-delimited JSONtext & code

application/x-ndjson

One JSON value per line — the format for streaming records, logs and bulk imports. Also called JSON Lines.

Good to know

No type is registered. application/x-ndjson is the de facto choice, and it's what Elasticsearch's _bulk API asks for. application/jsonl also shows up for .jsonl files.
Streaming APIs send one record per line as soon as it's ready. On the client, read the body as a stream, split on newlines and JSON.parse each complete line.
Not the same as application/json-seq (RFC 7464), which puts an ASCII record-separator byte (0x1E) before each record.

The response header to send:

Content-Type: application/x-ndjson

Most servers pick the type from the file extension. If yours sends the wrong one, map it explicitly:

nginx (inside the types block in mime.types)

application/x-ndjson ndjson jsonl;

Apache (.htaccess or server config)

AddType application/x-ndjson .ndjson .jsonl

Express

res.set("Content-Type", "application/x-ndjson");

Python

import mimetypes

mimetypes.add_type("application/x-ndjson", ".ndjson")
mimetypes.add_type("application/x-ndjson", ".jsonl")

HTML file input

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

See what a server sends for a file, and what type a local file really is by its contents:

curl -sI https://example.com/file.ndjson | grep -i '^content-type:'
file --mime-type file.ndjson

application/x-ndjson. You may also see application/jsonl, but application/x-ndjson is the one to send. The same type covers .jsonl.

Content-Type: application/x-ndjson. It compresses well, so let the server apply gzip or Brotli.

Related types