PasteCheck

What is PasteCheck?

PasteCheck is a free browser-based tool for developers. Paste your JavaScript, TypeScript, Python or HTML and every syntax error gets highlighted instantly. red for errors, yellow for warnings. Tap any highlighted line to see the exact issue description.

No sign up. No account. No ads. Just paste and see what's broken.

https://www.pastecheck.co.uk

The Problem It Solves

Quick code verification on the go is painful. Existing online tools are cluttered, slow, or desktop-only. Pasting into an AI gives inconsistent results. it misses things, rewrites your formatting, or gives you an essay when you just need to find the missing bracket.

PasteCheck does one thing: show you exactly what's wrong, instantly, in a clean mobile-friendly interface.

What It Detects

JavaScript & TypeScript

• Syntax errors with line-level highlighting

• Loose equality (== instead of ===)

• var usage, console.log, debugger, eval, alert left in code

• Empty catch blocks, thrown string literals

  Python

• Syntax errors via Lezer parser

• Mixed tabs and spaces (error)

• Inconsistent indentation style (warning)

• Bare except clauses, print without parentheses

• Mutable default arguments, wildcard imports

  HTML

• Unclosed tags, deprecated elements

• Void element misuse

• Missing lang, charset, title attributes

• Duplicate IDs, unlabelled inputs

• Inline event handlers, inline styles

• Embedded script blocks linted for JS issues

• Embedded style blocks checked for CSS misspellings

  CSS (embedded in HTML)

• Misspelled properties flagged with "did you mean X?" suggestions

• Covers 70+ common typos like colour → color, font-weigh → font-weight

Current Stats

• Launched: May 17, 2026

• Users in first 24 hours: 10

• Events in first 24 hours: 54

• Countries: US, UK, Australia

• Cost to build and host: £0

What's Next

I'm monitoring real user feedback before adding anything new. Version 2 will be driven entirely by what users actually ask for rather than what I think they want.

Longer term I'm exploring a Pro tier — more languages, saved history, bulk checking — but not until there's clear demand for it.

Honest Feedback Welcome

I know there are gaps. The JavaScript linter stops after the first critical syntax error. Python indentation level jumps aren't caught yet. HTML mixed-content detection isn't perfect.

If you try it and find something it misses — I want to know. Drop it in the comments or use the feedback button on the site.

(https://www.pastecheck.co.uk)