JSONL Viewer (VSCode Extension) — V1

Custom editor for .jsonl files focused on large-file performance.

Features

• Custom Editor for *.jsonl
• Table view (columns sampled from first N object rows)
• Virtual scrolling (TanStack react-virtual)
• Search
  • substring match on raw line
  • key:value match on parsed object
  • optional Filter mode (show only matches)
• Row expand
  • JSON tree
  • raw line
  • inline raw editing
• Error marking: parse errors highlighted + error message
• Large file support
  • builds a byte-offset line index (cached in VSCode globalStorage)
  • reads visible line ranges on-demand
• Tail -f / streaming append
  • watches file growth
  • incrementally extends the index
  • auto-follow when you are near the bottom
• Open in jsonl.co (with UTM)

Editing & Saving

Edits are tracked as a patch-map (lineNumber → rawLine). The file is rewritten on save (streaming) to support length changes safely.

• Apply an edit inside an expanded row
• Press Save button or Ctrl/Cmd+S
• Or press Discard to drop pending edits

Telemetry (optional)

• Default: off
• Settings:
  • jsonl.telemetry.enabled
  • jsonl.telemetry.level

If enabled, telemetry only sends anonymous usage events (no file content/path). See:

• PRIVACY.md
• FAQ.md
• docs/telemetry/vscode-plugin.md (repo root)

To enable telemetry in a build, you must provide a connection string via env var:

export JSONL_VIEWER_CONNECTION_STRING="<app-insights-connection-string>"

Dev / Debug

From repo root:

bun install --cwd packages/vscode-plugin
bun run --cwd packages/vscode-plugin build

Then in VSCode:

1. Open this repo
2. Run Run Extension (use launch.json below)
3. In the Extension Development Host, open any .jsonl file

Suggested .vscode/launch.json (repo root):

{
  "version": "0.2.0",
  "configurations": [
    {
      "name": "Run JSONL Viewer Extension",
      "type": "extensionHost",
      "request": "launch",
      "runtimeExecutable": "${execPath}",
      "args": [
        "--extensionDevelopmentPath=${workspaceFolder}/packages/vscode-plugin"
      ],
      "outFiles": [
        "${workspaceFolder}/packages/vscode-plugin/dist/**/*.js"
      ]
    }
  ]
}

Package VSIX

bun run --cwd packages/vscode-plugin package
# output: packages/vscode-plugin/big-jsonl-viewer.vsix

Install locally:

code --install-extension packages/vscode-plugin/big-jsonl-viewer.vsix

CI

GitHub Actions workflow: .github/workflows/vscode-plugin.yml

• Builds extension + webview
• Packages big-jsonl-viewer.vsix
• Uploads VSIX as artifact

Marketplace publish step is included as commented-out template.