I built a free developer toolkit that runs in your browser (UUID, Base64, regex, hashes)

I've been building a set of small developer tools at everydaytoolz.com. They do one job each, and nothing you paste is sent to a server.

UUID Generator: random UUID v4 values, one or many at a time.
Base64 Encoder/Decoder: Unicode-safe, so emoji and non-English text survive the round trip.
Regex Tester: tests a pattern against your text live, using JavaScript's built-in regex engine, with capture groups shown.
Hash Generator: MD5, SHA-1, SHA-256, SHA-384, and SHA-512 computed together.
Number Base Converter: binary, decimal, octal, and hex, converted at once.
IP Subnet Calculator: netmask, network and broadcast addresses, and the usable host range.
Markdown Viewer: side-by-side live preview.
File Size Converter: bytes, KB, MB, and GB in binary or decimal.
The tools are plain JavaScript on each page, with no account and no install. The regex tester uses your browser's engine, so the results match what your code will do in JavaScript. I'd like feedback, especially on anything that behaves differently from what you'd expect.