What tool should I build into GlaeKit next?

Launching GlaeKit here on Wednesday — a free set of browser-based tools for PDFs, images, and everyday dev tasks (JSON, Base64, QR codes, etc). Everything runs client-side, nothing gets uploaded.

Curious what's missing: what's a tool you find yourself reaching for a sketchy ad-filled site to use? Happy to add it if it's a good fit.