jlv

A terminal viewer for JSONL files (one JSON value per line).

https://github.com/user-attachments/assets/5e47dbae-dd43-408b-b65d-e8e98aeeba17

Install the jsonl-viewer package; the command is still jlv:

uv tool install jsonl-viewer
jlv your-file.jsonl

Alternatively, use pip install jsonl-viewer. From a source checkout:

uv run jlv your-file.jsonl

Requires Python 3.12+ and Textual 8+. The left panel lists numbered records; the right panel shows the selected record as indented JSON. Select a string to read its decoded contents in a scrollable, word-wrapped inspector.

Screenshots

Browse records alongside their formatted JSON:

Open a string to read its decoded, word-wrapped contents:

Controls

The inspector is read-only and supports text selection and Ctrl+C to copy. The main panels also support text selection. The left-hand preview is capped at 1,000 characters, but the right-hand document and decoded strings are not truncated.

Search

The main panels share one search across the full formatted JSON, including text beyond the left panel's truncated previews. A result selects its record on the left and highlights the matching text on the right, scrolling it into view. F3 and Shift+F3 (or n and N with a panel focused) move between individual matches, including matches in the same record, and wrap at either end of the file. Escape closes the search bar.

Inside the string inspector, search is independent and limited to that decoded string.

Search defaults to literal, case-insensitive matching. Use Alt+R for regular expressions and Alt+C for case-sensitive matching; the search bar displays both settings. Press Enter to search after editing the query or changing an option.

Large files

Both main panels render only visible rows, rather than creating a widget for every record or JSON field. The loader validates the entire file in one buffered pass and builds a compact byte-offset index. Records are read and parsed on demand; small bounded caches retain recent previews and formatted documents. The string inspector also renders a viewport, and defers wrapping until its actual display width is known.

Validation still happens before the viewer opens: malformed JSON, invalid UTF-8, and interior blank lines are reported with a line number. Trailing blank lines are permitted. This is a read-only viewer, not a live file follower; do not edit the input file while viewing it.

Sample file

The repository includes stress-test.jsonl.gz, a compressed synthetic dataset with 30,000 records. Extract it before opening it:

gzip -dk stress-test.jsonl.gz
uv run jlv stress-test.jsonl

The extracted file is 300 MB and is Git-ignored. Records range from approximately 1-100 KB and contain nested structures and strings of varying lengths. Some strings intentionally end mid-sentence to fit the generated record sizes.