JSON Lines / NDJSON Viewer

Paste a JSON Lines (a.k.a. NDJSON, .jsonl) stream — one JSON value per line — and see every line parsed with its line number, a validity flag, the raw text, and a pretty-printed value. Filter by kind, search by substring, evaluate a tiny dotted JSONPath ($.user.name, $.items[0].sku, $.items[*].sku), and export the filtered valid rows as NDJSON or a JSON array. Pure client-side, no upload, no tracking.

NDJSON input

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One JSON value per line. Blank lines and # … comments are tolerated. CR / CRLF / LF all work.

Kind filter

All Valid only Invalid only Valid + invalid

Substring search

JSONPath dotted: $.a.b[0] · wildcard: $.items[*].sku

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Copy as NDJSON Copy as JSON array Download .ndjson

How this works

• Each line is run through JSON.parse. Lines that parse cleanly are marked valid; lines that don't are marked invalid with the parser's error message and (when available) the column offset. Lines whose first non-whitespace character is # are treated as comments; empty and whitespace-only lines are treated as blank. None of these are errors — they're surfaced so you can see them.
• The kind filter at the top controls which rows show up in the table. All shows every line, Valid only hides blanks / comments / invalid lines, Invalid only shows just the parser rejections, Valid + invalid hides blanks and comments.
• Substring search is case-insensitive and matches against the raw line text (not the parsed value). JSONPath is evaluated against each valid row's parsed value and shown in the value column when present.
• JSONPath syntax: $ is the root; .key indexes into an object; [n] indexes into an array (negative indices allowed); [*] expands to an array of every match; and the two can be chained: $.items[*].sku. An invalid path disables the column (rather than throwing).
• Click the raw, pretty, or path chip on any row to copy it. Click a row's value cell to open the row in a detail pane (line number, raw, pretty-printed value, JSONPath result).
• Copy as NDJSON emits one JSON value per line, re-stringified with JSON.stringify so output is canonical (sorted keys not guaranteed, but whitespace / quoting always normalised). Copy as JSON array emits a single [ … ] document. Download saves the NDJSON output as ndjson.txt.
• The page is built on top of src/lib/tools/ndjson.ts — every function on this page is unit-tested (65 cases). Nothing leaves your browser.