Open files in VS Code and Cursor / Machine learning files

View a JSONL file as a table in VS Code

Install the free JSONL Viewer and click the .jsonl file. Each line becomes a row, with a column for each key and its type. Switch to Record view for one line as a tree, or Chat view to read fine-tuning and eval data as messages. A filter such as level == error and ctx.ms > 500 narrows the rows.

Install in VS Code Marketplace page Open VSX (Cursor, Windsurf, VSCodium)

Free, MIT license. Extension ID zovo.zovo-jsonl-viewer, version 0.2.3. Needs VS Code 1.90.0 or newer.

A 30,000 line NDJSON log filtered to 312 error records slower than 300 ms, sorted by timestamp, with the nested ctx object of one row opened as a tree.

Steps in VS Code

Install JSONL Viewer from the Marketplace, or press Ctrl+P (Cmd+P on macOS) and run ext install zovo.zovo-jsonl-viewer.
Click a .jsonl, .ndjson, .jsonlines or .jsonl.gz file.
Switch between Table, Record and Chat at the top right.
Type a filter and press Enter. Operators include ==, >, contains, =~ (regex), exists and missing.
Export the rows you see to CSV, a JSON array or JSON Lines.

Steps in Cursor, Windsurf or VSCodium

Open the Extensions view with Ctrl+Shift+X (Cmd+Shift+X on macOS).
Search for zovo.zovo-jsonl-viewer and click Install. Cursor, Windsurf and VSCodium install from Open VSX, where it is published as zovo/zovo-jsonl-viewer.
If your editor has no gallery, download the .vsix from the Open VSX page and run "Extensions: Install from VSIX...".
Then use it the same way as in VS Code.

What JSONL Viewer handles

Chat formats from OpenAI (messages), ShareGPT (conversations) and Gemini (contents), with tool calls shown in boxes.
In the test suite, a 40 MB file with 360,000 lines showed its first page in about 20 ms.
Bad lines are marked in red with their line numbers. Follow mode tails a growing log.

What it does not do

Files must be under 4 GB. Lines over 5 MB are cut in the table.
.jsonl.gz files are unpacked in memory up to 512 MB.
Use "Open as Text" to edit the raw lines.

Other options

jsonl-viewer (MBear.jsonl-viewer, 16,786 installs, not on Open VSX). Another JSONL viewer. Not on Open VSX.
jq. jq -c 'select(.level == "error")' file.jsonl filters lines in a terminal.

Install counts and Open VSX status were checked on 8 November 2026. Descriptions in quotes are the extensions' own.

Questions

Can I read OpenAI fine-tuning files as a conversation?

Yes. Chat view shows the system, user, assistant and tool messages of each record as bubbles.

How big a file can it open?

Up to 4 GB. It indexes the file as a stream and shows 200 rows at a time.

Does it work offline?

Yes. It makes no network calls and has no telemetry.

More about JSONL Viewer

Read the JSONL Viewer page for every feature and setting, or the source code on GitHub.

Support this work

If this extension saves you time, you can support the work on GitHub Sponsors. Monthly tiers start at $5, and one-time tiers start at $15. Sponsorship is optional, and the tool works the same without it.

Zovo on GitHub