JSONL Viewer
Open a JSONL or NDJSON file, including multi-GB ones, and scroll, search or jump to any line. The file stays on your computer, because everything runs in your browser.
Runs entirely in your browser. Your file is never uploaded. How this works
How it handles large files
Most browser tools read the whole file into memory, which fails or freezes on large files. This viewer scans the file once in a background thread and records where every 256th line starts. To show a line, it reads only that small section of the file. The index for a 5 GiB file is under 1 MB.
See the benchmark for measured results, or the guide on opening large JSONL files for other options.
How to use it
- Drop a
.jsonlor.ndjsonfile on the box above. - Scroll, or enter a line number to jump there.
- Click a line to see it as formatted JSON.
- Search for text to step through every matching line.
Frequently asked questions
- How large a file can this open?
- We tested a 5 GiB file with 15.6 million lines in Chromium. The viewer reads the file in pieces and keeps a small index rather than the whole file, so memory use stays low. Speed depends on your disk and browser.
- Is my file uploaded?
- No. The file is read locally by your browser. The site also sends a Content-Security-Policy header that makes the browser block fetch, XHR, WebSocket and beacon requests, which you can confirm in your browser’s developer tools.
- What is the difference between JSONL and NDJSON?
- In practice they are the same format: one JSON value per line. This viewer opens both.
- Does search support regular expressions?
- Not yet. Search finds plain text, with an option to match case. Case-insensitive matching applies to ASCII letters.