Dev tools that run 100% in your browser — your data never leaves the page

Most "free online dev tools" quietly POST everything you paste to a server. For API payloads, tokens, or customer data, that's a bad default.

A cleaner pattern: tools that do all the work client-side. The page loads once, then parsing/generating/converting happens locally — nothing is uploaded, no signup, and it works offline.

Here's a set that actually follows this. All have a free core; paid only unlocks bulk/export/history.

Runs entirely in your browser

• 
  — live match highlighting + a plain-English explainer; Pro exports the pattern as JS/Python.


• 
  — palettes + WCAG contrast; export CSS vars / JSON tokens.


• 
  — meta-tag audit + Google/social preview.


• 
  — summarize/rewrite/draft with AI that runs locally; nothing you type is uploaded.


• 
  Grimhollow — an AI dungeon master that runs fully offline after a one-time model download.

Why bother?

1. 
   Privacy by architecture — no server log to leak.


2. 
   No signup friction — paste, get the answer.


3. 
   Works offline — even the on-device-AI ones.

The trade-off is honest: free covers everyday use, paid adds bulk/exports/history. If you touch anything sensitive, in-browser tools are simply the safer default.

What in-browser tools do you reach for? Curious what I'm missing.