Regex, formatters, metadata and the files every repository needs.
Build a .gitignore from the stacks you actually run, with the lines that matter and none of the historical noise.
Every HTTP status code worth knowing, from 200 and 301 to 429 and 503, with a line on when to reach for it rather than a paraphrase of the RFC.
Format, validate, sort or minify JSON. Unquoted keys, trailing commas and comments are accepted, so a pasted console log works as well as a strict file.
Write the title, description and image once and get the full head, the Next.js metadata object, and a preview of the card people will actually see.
Test a JavaScript regular expression against real text, see every match highlighted in place, and read the capture groups out one by one.
Turn a one-line query into something reviewable: clauses on their own lines, joins indented under them, keywords in capitals.