Open JSONL and NDJSON files on Mac

Quick answer

JSONL and NDJSON are two names for the same line-delimited JSON structure. Slate Viewer opens .jsonl and .ndjson files locally on macOS 26.0 or later, with a structured reading view and search. When punctuation or escape sequences matter, check the original file in a plain-text editor.

Try a three-record JSONL example

Copy these fictional records into a plain-text file named run.jsonl. Keep each JSON object on its own line; the last record is the one to investigate.

{"time":"09:00","step":"ingest","status":"complete","items":3}
{"time":"09:02","step":"render","status":"complete","items":3}
{"time":"09:03","step":"review","status":"needs attention","items":1}

The third record flags one item for review. The file does not say what caused the warning.

JSONL vs NDJSON: the same line-delimited structure

For a well-formed JSONL file, use UTF-8 text with one complete, valid JSON value per line and no blank lines. A value can be an object, array, string, number, boolean, or null. The JSON Lines guide treats blank lines as invalid; the NDJSON specification allows parsers to ignore them when that behavior is documented. Follow your reader's documented behavior when handling blank lines.

Why these files are different from one JSON document

A regular JSON file usually contains one top-level value. A JSONL or NDJSON file contains a sequence of independent values separated by line breaks. That structure is common in AI result streams, data exports, and logs, where reading the records and checking the original text are both important.

Read a record, then check the original text

1. Open run.jsonl in Slate Viewer. Read the three records in its structured view.
2. Search for the event to investigate. Search for needs attention or review, then inspect the fields in that record.
3. Open the same file in a plain-text editor. Check the original JSONL text, including the value of items, quotation marks, commas, and any escape sequences. The sample's third physical line contains "items":1.

The structured view helps you understand a record. Use the text editor when you need exact source text or want to edit a record.

A reader, not a JSONL repair tool

Slate Viewer is useful when you need to review AI batch output, an export, or a log without pasting it into a website. It is not a schema validator, malformed-record recovery tool, converter, database client, or bulk data editor. Use a dedicated data tool when validation, transformation, or processing large datasets is the actual task.

Local by default

Slate Viewer opens JSONL and NDJSON files on your Mac. It does not upload document text, file paths, JSON fields, or clipboard contents to Slate Viewer servers by default. It is a file reader, not a cloud workspace or an AI assistant.

Before you buy

Slate Viewer is a paid Mac App Store app for Apple silicon Macs (M1 or later) running macOS 26.0 or later. Check the store listing for the current price in your region. Its role here is to read and search local JSONL or NDJSON records; keep a text editor or data tool for exact source checks and data changes.

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