JSONL Gazelle

Fast JSONL viewer / editor for VS Code with advanced features including Table View and Pretty Print view. JSONL (JSON Lines, also known as NDJSON — newline-delimited JSON) is increasingly important for machine learning datasets, log analysis, data streaming, and LLM training. Unlike regular JSON, it can be processed line-by-line making it perfect for large datasets. Also works for NDJSON.

What's new

• v0.7.0: The cell cursor now reaches the headers — arrow up into a column header and press S to cycle its sort, arrow left into a row number and press U / D to move that row or Delete to remove it. A hint names the keys as you arrive, then fades
• v0.6.3: Spreadsheet keyboard navigation in Table View — arrow keys move a cell cursor, Enter edits it, Tab advances to the next cell
• v0.6.2: Sort by column, with timestamps and currency amounts detected automatically; hidden columns are now counted on the row-number header and unhidden with one click
• v0.6.1: Updated dependencies
• v0.6.0: File stats popover (record count, column count, file size); "Unhide Column" context menu to restore hidden columns; improved toolbar layout and stability
• v0.5.2: Faster loading for large files
• v0.5.1: Reduced package size
• v0.5.0: Diff view; export to CSV; AI add now supports for Anthropic, Gemini, Ollama; persistent settings; various fixes
• v0.4.3: Line-by-line navigation in Raw and Pretty print mode, fixed small bugs, updated models.
• v0.4.2: Fixed AI settings persistence so model/system prompt changes are saved even when the API key remains unchanged.
• v0.4.1: Improved editing reliability with row/insertion ordering fixes, safer autosave behavior, and less intrusive rating prompts.
• v0.4.0: Added AI-powered column suggestions from the context menu, manual column insertion improvements, and row filtering mapping tests.
• v0.3.4: Improved AI settings flow when API keys are missing, plus dialog polish and stability fixes.
• v0.3.1: Added a Split into Parts (100MB+) command in the file context menu for very large JSONL files.
• v0.3.0: Added a substantially improved Pretty Print view with syntax highlighting.
• UX updates: Added support for light themes and documented keyboard shortcuts for Pretty Print entry navigation (Ctrl+Alt+↑/↓, or Cmd+Option+↑/↓ on macOS) plus line move shortcuts (Alt+↑/↓, or Option+↑/↓ on macOS).

Features

• Fast Table View: Automatically detects common JSON paths and displays them as table columns
• Smart Column Detection: Maps common subpaths of each JSONL row into table columns automatically
• Column Expansion: Click ▼ to expand objects/arrays into separate columns (e.g., user.name, orders[0])
• Column Management: Right-click context menu on table headers to add, remove, or toggle column visibility. Hidden columns are counted by a badge on the row-number header — click it to bring them back
• Spreadsheet Keyboard Navigation: Click any cell in Table View to place a cell cursor, then drive the table from the keyboard — arrow keys move a cell at a time, Enter edits the cell under the cursor, Tab advances to the next one
• Keyboard Header Actions: Arrow off the top of the grid onto a column header and S cycles that column's sort; arrow off the left onto a row number and U / D move that row up and down the file while Delete removes it. A hint appears with the cursor to name the keys, and fades once you have read it
• Sorting: Right-click a column header and open the Sort submenu — Display Sorted reorders just the view and leaves the file alone, Sort Rows reorders the file itself (undo with Ctrl/Cmd+Z). Values are typed automatically, so timestamps sort chronologically and amounts like $1,200.00 sort by value rather than as text
• JSONL-Aware Diff: Diff a file against Git HEAD or another JSONL file with row alignment and field-level change highlighting — edited rows show exactly which fields changed (old → new) instead of a wall of raw JSON
• Memory Efficient: All processing happens in-memory without creating separate files
• AI Features: Generate columns and rows with AI using OpenAI, Anthropic, Google Gemini, or a local OpenAI-compatible server (Ollama, LM Studio, vLLM, ...) — model lists are fetched live from each provider

Usage

1. Open any .jsonl or .ndjson file in VS Code
2. The file will automatically open in the JSONL Gazelle viewer
3. Table View: Click ▼ buttons in column headers or double-click expandable cells to expand objects/arrays into separate columns
4. Table View keyboard navigation: Click a cell (or press an arrow key) to place the cell cursor, then use ↑ ↓ ← → to move a cell at a time, Home / End for the first/last column, Page Up / Page Down for a screenful of rows, Enter (or F2) to edit the cell, Tab / Shift+Tab to move to the next/previous cell, and Esc to put the cursor away. While editing, Enter saves and steps down a row, Tab saves and steps to the next cell, and Esc discards the edit
5. Table View header actions: keep pressing ↑ past the first row to put the cursor on a column header, where S cycles that column's display sort (ascending → descending → off). Press ← past the first column to put it on a row number, where U and D move that row up and down the file and Delete removes it (moving is unavailable while the view is display-sorted, since screen order and file order no longer match). Both headers show a hint naming their keys, which fades after a few seconds
6. Pretty Print view: You can edit inline
7. Pretty Print navigation: Use Ctrl+Alt+↑ / Ctrl+Alt+↓ (Cmd+Option+↑ / Cmd+Option+↓ on macOS) to jump between JSONL entries
8. Raw view navigation: Use Ctrl+Alt+↑ / Ctrl+Alt+↓ (Cmd+Option+↑ / Cmd+Option+↓ on macOS) to jump to the previous/next JSONL line
9. Move current line: Use Alt+↑ / Alt+↓ (Option+↑ / Option+↓ on macOS) to move the current line up or down in the editor
10. Diff view: Run JSONL Gazelle: Diff with Git HEAD (command palette, editor title button, or right-click in the Explorer / Source Control view) to see uncommitted changes with per-field highlighting; use JSONL Gazelle: Compare with JSONL File... to compare two files. Click a modified row to see the full before/after JSON, and click a ⋯ unchanged lines separator to reveal hidden context

Extension Development

1. Clone this repository
2. Run npm install to install dependencies
3. Run npm run compile to build the extension
4. Press F5 to run the extension in a new Extension Development Host window

Test Data Generation

For testing with large datasets, you can generate a comprehensive test file with 45,000 lines (~64MB) containing varied fields and nested structures:

# Generate large test data file
cd test-data
node generate-large.js

This will create test-data/large.jsonl with:

• User profiles with nested addresses, preferences, and social media links
• Orders with items, pricing, shipping, and tracking information
• Analytics data with metrics, device info, and campaign details
• Log entries with request details, performance metrics, and error information
• Mixed data types: strings, numbers, booleans, arrays, objects
• Nested structures up to 4-5 levels deep

The generated file is automatically excluded from git via .gitignore to keep the repository lightweight.

What's next / Roadmap

• [ ] LLM / chat-format awareness: detect messages: [{role, content}] rows and render them as a conversation, with format validation for fine-tuning and eval files
• [ ] Row detail side panel: a resizable panel showing the selected row as pretty-printed JSON, so large fields stay readable without widening the table https://github.com/gaborcselle/jsonl-gazelle/issues/38
• [ ] Column profiling / stats popover: per-column type distribution, null rate, distinct count, min/max/mean, and top values from the header context menu

License

MIT License. See LICENSE file for details.