Big JSONL Viewer for VS Code

Open .jsonl and .ndjson files as a fast, searchable table — right inside your editor. Built for files that are too big to scroll and for logs that are still being written.

Install

Get it on the VS Code Marketplace

Or from the command line:

code --install-extension rootfily.big-jsonl-viewer

Or open the Extensions panel in VS Code and search for “Big JSONL Viewer”.

Free, MIT licensed.

Why an extension, when this site already opens big files?

Because they solve different halves of the same problem. jsonl.co is for a file you have in hand right now: drag it in, look at it, convert it, leave. The extension is for files that live where you work — in your repo, on a server you are SSH'd into, inside a container.

Logs that are still growing

A browser only ever sees a snapshot of the file you picked. The extension watches the file on disk, extends its index as new lines land, and follows the tail the way tail -f does.

Edit and save in place

Fix a malformed line and press Cmd+S. The file is rewritten by streaming, so a change in line length is safe even on a multi-gigabyte file.

Wherever the file already is

Remote-SSH, Dev Containers, WSL — the extension runs where your code runs. No copying a 4 GB log to your laptop to read three lines of it.

What it does

Table view
Columns are sampled from the first rows and rendered with virtual scrolling, so a million-line file scrolls like a short one.
Search and filter
Substring match on the raw line, or key:value match on the parsed object. Filter mode hides every row that does not match.
Parse errors in place
Malformed lines are highlighted where they are, with the parser's own message. No more bisecting a file to find the bad row.
Built for huge files
A byte-offset line index is built once and cached, then only the visible range is read from disk. Opening is instant regardless of size.
Expand any row
See the parsed JSON as a tree, the raw line as text, and edit it inline.
Nothing leaves your machine
The file is read from disk and rendered in a sandboxed webview. No uploads, no network calls, and telemetry ships disabled.

FAQ

Does it work with .ndjson files?

Yes. NDJSON and JSONL are the same format under two names, and the extension treats them identically. It registers as the editor for .jsonl files; for .ndjson or .txt, use “Open With…” and pick JSONL Viewer.

How large a file can it open?

Multi-gigabyte files are the design target. The extension builds a byte-offset index of line positions, caches it, and then reads only the rows you are actually looking at, so memory use stays flat as the file grows.

Does it send my data anywhere?

No. The file is read from disk and rendered in a CSP-restricted webview that cannot make network calls. The extension works in VS Code's Restricted Mode and never executes code from your workspace. Optional usage telemetry is disabled by default.

Can I edit files, or is it read-only?

You can edit. Expand a row, change the raw line, then save with Cmd+S or the Save button. Edits are tracked as a patch map and the file is rewritten by streaming, so lines can grow or shrink safely.

Does it work over Remote-SSH or in a container?

Yes. It runs on the machine that holds the file, which is the point — you can read a log on a remote server without copying it down first. Virtual filesystems are not supported, because the line index needs byte-offset access to a real file.

Just need a quick look or a conversion?

The tools on this site run entirely in your browser — no upload, no sign-up. Use them for one-off conversions and validation, and keep the extension for files that live in your project.

Browse the JSONL tools