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NDJSON Tools

Validate line by line, convert to and from a JSON array, filter records with a JSONPath query, or summarise what is actually in the file. One JSON value per line — the format log pipelines and data exports use, and the one a normal JSON parser refuses.

Input
Validation report 
Result will appear here
Filtering

JSONPath over the record list

In filter mode $ refers to the list of records, so the familiar array form works and you can pull a slice out of a log without loading it into anything:

$[?@.level == "error"]          records whose level is error
$[?@.status >= 400]             failing requests
$[?@.user.id == 4172]           a nested comparison
$[?@.error]                     records that have an error field at all
$[?match(@.path, "/api/.*")]    path matching, using RFC 9485 I-Regexp

Queries are evaluated by the same RFC 9535 engine that scores 703/703 on the official compliance suite, so comparisons are strictly typed — @.status == "404" will not match the number 404. Lines that do not parse are skipped and counted rather than stopping the filter, which matters on a log where one truncated line should not cost you the rest of the file.

What it handles

The things real files contain

Blank lines and CRLF

Blank lines are ignored, as the format requires, and counted so you know they were there. Windows CRLF endings and lone CR are both handled, and reported.

A byte order mark

PowerShell's Out-File and several Windows editors add one. It is skipped rather than breaking the first record, and mentioned so you can strip it at the source.

Large integers

Converting to an array copies each record's text rather than re-serialising it, so a 64-bit ID survives exactly instead of being rounded through an IEEE 754 double.

Standards

What defines NDJSON

Nothing at the IETF. NDJSON is described by the ndjson specification and by jsonlines.org, which agree with one another: UTF-8, one JSON value per line, newline separated, blank lines ignored.

It is worth not confusing it with RFC 7464 — JSON Text Sequences, which solves the same problem with a 0x1E record separator instead of a newline and carries the media type application/json-seq. Either way each record itself follows RFC 8259.

Related

Where to go next