jlv

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

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.

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.