jsonl.co

jsonl.co is an online viewer and editor for JSONL (JSON Lines / NDJSON) files, built for the large files that make most tools freeze. It streams files in chunks and renders only the visible rows, so datasets of 1GB and more open quickly in the browser. Everything runs locally: files are never uploaded and there is no account to create, which makes it a safe choice for sensitive data such as AI training sets and production logs. Drop a file, paste text or type JSONL to see raw lines on the left and parsed JSON on the right, with synchronized scrolling, syntax highlighting and real-time line-by-line validation. Edit or delete lines, use find and replace, and export with one click. It supports .jsonl, .ndjson, .json and .txt files. The site also offers in-browser converters between JSONL and JSON, CSV, Excel and YAML, plus a formatter, validator, splitter, merger and JSON flattener, along with guides on JSON vs JSONL and OpenAI fine-tuning formats. It is available in 12 languages and has a companion VS Code extension.