The Tools
How the tools work, why they refuse to guess, and what runs on your device.
A hex colour is three bytes written in base 16, and once you can read it #1a2b3c stops being opaque. Including why the shorthand #abc expands to #aabbcc and not #0a0b0c.
A gradient is one multiplication per channel repeated across a line. Why a gradient between two channel-opposite colours always passes through grey, and what moving a stop really changes.
Four lines go in your head and they have four different jobs — one of which is nothing. The keywords tag stopped being read by the major search engines many years ago.
JSON-LD tells a machine what a page is. It does not raise anything by itself — what it can do is make a result eligible for a richer presentation, and only if it matches what a reader can see.
The cut-off is a width in pixels, not a count of characters — so a line of wide letters runs out sooner than a line of narrow ones. Front-loading beats hitting a number.
Flesch counts sentence length and syllables, and calls that difficulty. It is a proxy — a text can score beautifully and still be incomprehensible.
Nothing the policy refuses announces itself, and a local server that sends no policy at all will look perfect right up until you deploy.
Framing, MIME sniffing, referrer leakage and forced HTTPS — four narrow jobs. Worth doing, and worth knowing exactly how narrow each one is.
A disallowed URL can still show up in search results, and the noindex tag that would keep it out only works if the crawler is allowed to fetch the page.
A 301 gets cached by browsers, sometimes with no expiry, and undoing one means reaching machines you do not control. Also: why two hops usually means one too many.
It is one integer: seconds since 1970 in UTC. Every time-zone bug and every accidental trip to the year 57971 comes from what happens after that.
Luhn is a checksum for catching typos. It says a string of digits is internally consistent — not that an account exists, and not that anyone owns it.