Paste a raw Cookie header — the k1=v1; k2=v2 string your browser or server sends — and it is split on semicolons into a clean key-value table and an equivalent JSON object. Surrounding spaces are trimmed, and URL-encoded values are decoded so you can read them directly, while duplicate names are kept.
Reverse the process by pasting a flat JSON object of name-value pairs to rebuild a single Cookie header string ready to drop into a request. Everything runs locally in your browser — session cookies and tokens are never uploaded to any server.