JSONL Lens

open a .jsonl or .ndjson file and click Open in JSONL Lens, the table icon at the top right of the editor, or right-click the file or its tab and choose Open in JSONL Lens.

a fast viewer for jsonl and ndjson files of any size. use it as a jsonl viewer: each record is a row, each field a column. records are indexed by byte offset in one pass and read on demand, so a multi-gigabyte training set is on screen while its index builds and the file is never loaded whole into memory. the viewer is free: grid, find with regular expressions, schema tab, record detail. pro, a subscription, adds whole-file filter queries, export, exact stats and grid themes, and it is on from the first open: each machine gets a 30-day pro trial with no key to enter, and the status bar counts it down from "Pro trial, 30 days left". in Cursor, Windsurf and VSCodium, install it from Open VSX.

Free - the full viewer, for files of any size

• Any size: a line index built in one pass, with live progress; browse records while indexing runs. a 1.02 GB, 5,000,000-record file indexes in 3.7 s on a laptop with an NVMe drive.
• Gzipped too: a .jsonl.gz or .ndjson.gz opens the same way. it is unpacked once to a temp file that is deleted when the tab closes, the progress bar shows the unpacking, and the status line names the unpacked size beside the compressed one.
• Find in file: full-text search across every record, or a regular expression tested against each record on its own; case toggle, next/previous jump between matching records, matches only to page through the hits alone - built on the same one-pass scan, so it works on multi-gigabyte files.
• Go to row: type a record number, Enter, and the grid is there (Ctrl+G for the box).
• Grid view: records as rows, fields as columns - column set derived from a sample of the file, nested fields as dot-paths like user.plan.
• Schema tab: every field path seen in a sample of the file, with present, missing and null counts, types, min, max, average, distinct strings and example values.
• Record detail: the selected record pretty-printed with key order and int64 precision preserved; copy is one click.
• Bad lines: malformed lines, blank lines, CRLF endings and oversized records are reported and skipped; the rest of the file still reads.
• Reads in place: a plain file is read where it is, not copied or converted; the index is a list of byte offsets kept in memory and thrown away when the tab closes.
• Private: runs locally. no account, no telemetry. the free viewer makes no network calls; a key makes one activation call when you paste it, a license check about once a week after that, and one release call when you remove it. the trial start is kept in .twilightventures-lens.json in your home folder as well as in VS Code.

every record in the file is indexed, at 8 bytes a record, and the index holds over four billion; search reads every record, and the grid asks for records in pages of 200 as you scroll. in the grid a nested object is flattened into dot-path columns, so meta.source is a column of its own, and a value that is itself an object or an array shows as one-line JSON in its cell; the columns are the twelve most present field paths in the sample, and the record detail shows every field. the extension runs on VS Code 1.90 or newer. only .jsonl, .ndjson, .ldjson and .jsonlines files are claimed, gzipped or not, and plain .json is not; the text editor stays the tab that opens first: JSONL Lens is the Open With choice and the Open in JSONL Lens command. the status bar item shows only while a JSONL Lens tab is active; the pro dialog appears only when you click a pro item.

Pro, optional subscription

• Whole-file filter queries: level == "error" && status >= 500, tested against every record in the file; the grid becomes the matching set.
• Export: all records, filter matches or search matches, to jsonl or csv, with a cancelable progress bar. never over the source file.
• Exact stats: the schema tab's full scan computes its stats from every record instead of a sample.
• Themes: twelve looks for the grid: default, hacker, cyberpunk, goblincore, neon, nosferatu, halloween, blue lagoon, duskhollow, abyss, obsidian and moonlit garden, each tuned for light and dark editors. run JSONL Lens: Pick theme to try one; trying is free for the window, keeping it is pro. the default look never changes.

the trial has four notices, each shown when a JSONL Lens tab is in front. one comes inside the last seven days, with the days left in it rather than seven every time, and another on the final day; those two stay out of a sitting that asks you for a review, and never both show in one session. a third comes once the trial has ended. it reads "Your Lens Pro trial has ended. Get Lens Pro to keep whole-file filters, export, exact stats and themes.", and after it the free viewer stays as it was. the fourth comes first, when the trial starts: "Lens Pro is on for 30 days on this machine: whole-file filters, export, exact stats and themes. No key needed.". a machine sees each of the four once, and a key entered stops all of them. all four carry two buttons, Buy (personal) and Business pricing, which open the two checkouts of the Get Lens Pro pick in the status bar menu. the other three start with what the trial did, as in "This trial: 3 filter queries, 1 export.", and all four end with the price. besides those, the first time a filter query, an export or a full-file stats run produces something during the trial, with more than seven days of it left, one plain message names it, as in "That filter query was Pro. Your trial runs 27 more days. Search stays free."; it comes once and has no button. every pro dialog names the feature, "Whole-file filter is a Lens Pro feature." for the filter box, ends with the price and offers three buttons, Buy (personal), Enter license key and Business pricing; an export or a full-file stats run turned down leaves the same price line in a note on the grid. the command palette has the pair as JSONL Lens: Get Lens Pro and JSONL Lens: Enter license key, and the status bar item opens a menu with both and Write a review.

one Lens Pro key covers JSONL Lens, Parquet Lens and Log Lens for VS Code, but the three do not pass the key between them. paste it into each one you use; the Remove license key command in that extension releases that activation again.

$4.90 a month or $49 a year personal, $9.90 a month or $99 a year business: one key for all three extensions, and Pro stays on in every build while the subscription runs. a personal key activates on up to 3 machines, a business key on 10, all three extensions on each (each extension on each machine is one activation: 9 on the personal key, 30 on the business key); release a machine from the Polar customer portal. when the subscription ends, Polar revokes the key and Pro turns off at the extension's next check, about once a week; the free viewer stays.

buy on polar (personal, business), then run JSONL Lens: Enter license key.

receipts, invoices, your subscription, your key and its activations are in the Polar customer portal at polar.sh/twilight-ventures/portal; cancel there any time. sign in with the purchase email. for a refund, write to support@twilightventures.dev. a refund revokes the key.

the free viewer is the complete viewer, not a demo. everything that was free in 0.1.0 stays free in every later build; pro adds the four items above and nothing is taken away.

Part of the Lens family

• Parquet Lens for VS Code: the same grid, find and schema tab for Parquet, Avro, TFRecord, Arrow and Feather files; a jsonl export from it opens straight here.
• Log Lens for VS Code: the same grid and find for log files, with a filter per level; a jsonl export from it opens straight here.
• On JetBrains IDEs: JSONL Lens, Parquet Lens and Log Lens - one engine, a shared filter grammar, exports that open in each other.

Guides and support

the guides and the family overview are at twilightventures.dev. write to support@twilightventures.dev about anything to do with JSONL Lens or a purchase, suggestions included; for a bug, name the version and the rough size of the file. bugs and requests can also go on the issues page of the Lens repository.

in your language

한국어: JSONL Lens는 크기에 상관없이 .jsonl과 .ndjson 파일을 VS Code에서 엽니다. 레코드는 한 번의 스캔에서 바이트 오프셋을 기준으로 인덱싱되고 필요할 때만 읽히므로, 수 GB 파일도 인덱싱이 끝나기 전에 화면에 나타나고 메모리에 통째로 올라가지 않습니다. 뷰어는 그리드, 정규식 검색, 스키마 탭, 레코드 상세까지 무료입니다. 구독형 Pro는 파일 전체 필터 쿼리, 내보내기, 정확한 통계, 그리드 테마를 추가하며, 처음 열 때부터 켜져 있습니다. 컴퓨터마다 30일 Pro 체험이 라이선스 키 입력 없이 시작됩니다. 확장이나 구매에 관한 문의와 제안은 한국어로 보내 주셔도 됩니다 (support@twilightventures.dev).

**中文：**JSONL Lens 可在 VS Code 中打开任意大小的 .jsonl 和 .ndjson 文件。记录在一次扫描中按字节偏移建立索引、按需读取，因此数 GB 的文件在索引完成前就已显示，且不会整个加载到内存。查看器免费：表格、正则表达式查找、Schema 标签页、记录详情。订阅制的 Pro 版增加全文件过滤查询、导出、精确统计和表格主题，并且从第一次打开起就已启用：每台机器都有 30 天 Pro 试用，无需输入许可证密钥。关于扩展或购买的问题和建议，欢迎用中文发邮件至 support@twilightventures.dev。

**日本語：**JSONL Lens は、サイズを問わず .jsonl と .ndjson ファイルを VS Code で開きます。レコードは一度の走査でバイトオフセットを基準にインデックス化され、必要なときだけ読み込まれるため、数 GB のファイルでもインデックス作成を待たずに表示され、メモリに丸ごと載ることはありません。ビューアーはグリッド、正規表現検索、スキーマタブ、レコード詳細まで無料です。Pro（サブスクリプション）はファイル全体のフィルタークエリ、エクスポート、正確な統計、グリッドテーマを追加し、最初に開いたときから有効です。各マシンで 30 日間の Pro トライアルが、ライセンスキーの入力なしで始まります。拡張機能や購入についてのお問い合わせやご提案は、日本語でも support@twilightventures.dev までお送りいただけます。

Türkçe: JSONL Lens ile .jsonl ve .ndjson dosyaları, boyutu ne olursa olsun VS Code'da açılır. Kayıtlar tek geçişte bayt offset'ine göre indekslenir ve gerektikçe okunur; bu sayede birkaç GB'lık bir dosya indeksleme bitmeden ekrana gelir ve belleğe bütünüyle yüklenmez. Görüntüleyici ücretsiz: tablo, düzenli ifadeyle arama, şema sekmesi, kayıt ayrıntısı. Pro, abonelikle satın alınır; tüm dosya üzerinde filtre sorguları, dışa aktarma, kesin istatistikler ve tablo temaları ekler. İlk açılıştan itibaren her makinede 30 günlük Pro denemesi, lisans anahtarı girmeden kendiliğinden başlar. Uzantı veya satın almayla ilgili sorularınızı ve önerilerinizi Türkçe de yazabilirsiniz: support@twilightventures.dev.

Português: O JSONL Lens abre arquivos .jsonl e .ndjson de qualquer tamanho no VS Code. Os registros são indexados por offset de byte em uma única passagem e lidos sob demanda, então um arquivo de vários gigabytes aparece na tela antes de a indexação terminar e nunca é carregado inteiro na memória. O visualizador é gratuito: grade, busca com expressões regulares, aba de schema, detalhe do registro. O Pro é vendido por assinatura e acrescenta consultas de filtro no arquivo inteiro, exportação, estatísticas exatas e temas de grade, e já vem ativo desde o primeiro uso: cada máquina ganha um teste gratuito de 30 dias do Pro sem digitar nenhuma chave de licença. Dúvidas e sugestões sobre a extensão ou uma compra podem vir em português para support@twilightventures.dev.

Deutsch: JSONL Lens öffnet .jsonl- und .ndjson-Dateien jeder Größe in VS Code. Die Datensätze werden in einem Durchlauf nach Byte-Offset indexiert und bei Bedarf gelesen, sodass eine mehrere Gigabyte große Datei schon vor dem Ende der Indexierung angezeigt wird und nie vollständig im Speicher liegt. Der Viewer ist kostenlos: Tabelle, Suche mit regulären Ausdrücken, Schema-Tab, Datensatzdetails. Pro gibt es im Abonnement; es ergänzt Filterabfragen über die ganze Datei, Export, exakte Statistiken und Tabellendesigns und ist vom ersten Öffnen an aktiv. Jeder Rechner bekommt eine 30-tägige Pro-Testphase, ohne dass ein Lizenzschlüssel eingegeben werden muss. Fragen und Anregungen zur Erweiterung oder zum Kauf gern auf Deutsch an support@twilightventures.dev.