JSONL Viewer

Open and view JSONL and NDJSON files online. Inspect each JSON record, search data, and identify invalid lines directly in your browser.

Updated October 7, 2026

What is the JSONL Viewer?

JSON Lines (JSONL) and Newline Delimited JSON (NDJSON) are widely used for streaming logs, data pipelines, database dumps, and AI model training datasets. Unlike standard JSON files that enclose objects in a single top-level array, JSONL files store each valid JSON object on its own individual line. When opened in conventional text editors or standard JSON formatters, JSONL files often fail to parse or cause severe performance lag due to missing commas and lack of surrounding array brackets. The JSONL Viewer provides a fast, client-side interface designed specifically for JSON Lines data. Upload .jsonl or .ndjson files or paste raw line-delimited data directly to parse every line independently. Inspect records individually, expand complex nested trees, filter out malformed lines, and perform instant searches across your entire dataset—all processed safely inside your browser.

The JSONL Viewer operates 100% client-side in your web browser using modern JavaScript stream handling. Here is how your data is processed: 1. Line Segmentation The raw input text or dropped file content is split line-by-line using standard line break delimiters (\r\n or \n). Blank or whitespace-only lines are ignored automatically without triggering parsing errors. 2. Independent Record Validation Each non-empty line is parsed individually using native JSON.parse(). Valid Lines: Extracted into structured JavaScript objects ready for interactive tree inspection and field navigation. Invalid Lines: Trapped immediately without failing the rest of the document. The exact line number and parse error message are isolated for instant debugging. 3. Client-Side Security & Privacy No data is ever transmitted over the network. Files dropped into the viewer are read locally into browser memory via the FileReader API, ensuring sensitive API logs, database exports, and proprietary data remain completely private. 4. Search and Status Filtering Search queries perform instantaneous, case-insensitive string matching across raw line records. You can filter the view to display all records, valid records only, or isolate invalid lines to pinpoint syntax mistakes in corrupted datasets.

Parsing structured user activity event records in JSON Lines format.

{"event": "login", "userId": 101, "timestamp": "2026-06-25T10:00:00Z"}
{"event": "purchase", "userId": 101, "item": "subscription", "amount": 29.99}

Parsed 2 valid JSONL records with expandable tree inspection, search indexing, and zero invalid lines.

Detecting syntax errors on broken lines within large log exports.

{"status": "ok", "code": 200}
{"status": "error", "code": 500,}
{"status": "pending"}

Found 2 valid records and flagged Line 2 as invalid JSON (trailing comma error).

What is the difference between JSONL, NDJSON, and standard JSON?

Standard JSON wraps multiple data objects inside a single root array or object separated by commas (e.g., [{}, {}]). JSONL (JSON Lines) and NDJSON (Newline Delimited JSON) store each valid JSON record on a separate line without outer brackets or separating commas. This structure enables loggers and streaming systems to append data continuously without re-parsing the entire file.

Are my JSONL files uploaded to any external server?

No. The JSONL Viewer processes files in your browser. Whether using it complies with your organization's security policies depends on those policies and your environment.

How does the tool handle broken or invalid JSON lines?

Unlike traditional JSON validators that stop execution on the first error, this viewer parses each line independently. If a line contains malformed syntax (such as missing quotes or trailing commas), it flags that specific line number with an error description while continuing to parse and display all surrounding valid records.

What is the maximum file size this viewer can process?

Because processing occurs entirely in client-side browser memory, the viewer supports files up to 20 MB efficiently. For datasets larger than 20 MB, it is recommended to slice the file using command-line tools like head or split before opening.

Can I search for specific fields or values in my JSONL data?

Yes. Use the built-in search bar to filter records in real time. The viewer instantly matches search strings against raw line content across all records without requiring complex query syntax.

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