Webtools
Guides
Longer write-ups on the formats and mechanisms behind the tools — the parts that are easy to use without understanding and then surprise you later. Each one stands on its own; none of them require using a tool on this site.
Base64, Base64URL, and the padding problem
Why Base64 has two incompatible alphabets, what the = padding is for, and how to convert between the standard and URL-safe variants without corrupting data.
What's inside a JWT — and what it doesn't protect
A JWT is three Base64URL segments anyone can read. What each part contains, which claims actually mean something, and the difference between decoding a token and verifying it.
Reading a cron expression
The five fields, the step and range syntax, the day-of-month/day-of-week rule almost everyone gets wrong, and how daylight saving quietly skips or repeats jobs.
Choosing a hash function: MD5, SHA-1, SHA-256, and passwords
Which hashes are broken and for what, why a fast hash is the wrong tool for passwords, what length extension means for HMAC, and how to pick one for checksums, signatures, or storage.
UUID versions, and what they do to a database index
What the version and variant bits mean, how much entropy a v4 really has, why random UUIDs hurt B-tree inserts, and what UUIDv7 changes.
Percent-encoding: what to escape in a URL, and where
Reserved versus unreserved characters, why the rules differ per URL component, the difference between encodeURI and encodeURIComponent, and where the + for space myth comes from.