A few days ago I launched PasteCheck — a free tool
to paste code and see errors highlighted instantly.

After launch I found real gaps and shipped v1.3.
Here's what changed:

Python indentation monitor
Now flags mixed tabs and spaces as an error, and
inconsistent indentation style across the file as
a warning.

CSS property validator
Embedded CSS inside HTML now checked for misspelled
properties. Catches things like colour instead of
color, font-weigh instead of font-weight —
with "did you mean X?" suggestions.

Aria-label support
Previously flagged inputs with aria-label or
aria-labelledby as unlabelled. Fixed — those are
now correctly recognised as labelled.

Language detection confidence UI
Short snippets under 5 lines now show a subtle ?
badge next to the detected language so users know
detection may be approximate.

All shipped in a single session, tested, live.

Try it: https://www.pastecheck.co.uk

What would you want to see in v2?