I build AI agents and got tired of squinting at raw JSONL chat logs. Existing online viewers either choke on JSONL or upload your data. So I made one that runs offline in a single HTML file. Paste JSONL → auto-formatted with syntax highlighting. Auto-expands nested JSON strings (common in tool-call args). Toggle to render \n as real line breaks for reading embedded markdown/code. It's just one HTML file — open DevTools to inspect, Ctrl+S to save your own copy and modify however you like. https://tasks.hamsterbase.com/jsonl-viewer/