A free online toolbox that never uploads your files
The short version
I put together a site called ToolStack — 32 small everyday utilities in one place, all of which run entirely inside your browser. No account, no upload, no paywall. The interface is available in 7 languages.
The one-line pitch: paste or drop something, get the result, close the tab. Nothing you typed or dropped was ever sent anywhere.
What's actually in it
Worth listing, because "toolbox" sites often hide the good stuff behind a footer link:
Text and data
JSON formatter (2 / 4 spaces / tab, with syntax highlighting and line numbers)
JSON validator — reports line, column and character offset, not just "invalid"
Base64 encode / decode
Word and character counter
Images
Image compressor (quality slider, optional resize, before/after sizes)
Image cropper
Image resizer
Converters: JPG → PNG, JPG → WebP, PNG → JPG, WebP → JPG, HEIC → JPG
Colour and CSS
Colour picker
Colour converter
HEX ⇄ RGB, both directions
Gradient generator
CSS colour generator
Contrast checker (WCAG pass/fail on foreground/background pairs)
Units
General unit converter
cm ⇄ inches (both directions), kg ⇄ lb, miles ⇄ km
Everyday maths
BMI, discount, tip, percentage and age calculators
Countdown timer
Getting things done
QR code generator
Password generator
(all of the above, no sign-up required)
Why "no upload" is the point rather than a slogan
Most online tools for images and text are thin wrappers around an upload. You drop a file, it travels to somebody's bucket, a server processes it, and a download link comes back. For a stock wallpaper, fine. For a screenshot with a customer's address in it, an ID photo, a draft design that hasn't shipped, or an API response containing tokens — that's a bad trade for something your laptop could have done in 40 milliseconds.
ToolStack does the work locally: images are decoded and re-encoded by the browser's own Canvas machinery, JSON is parsed by the browser's own JSON.parse, and the rest is arithmetic in the page. There is no server endpoint that accepts your content, because there is nothing for it to send.
Three honest caveats, because a tool that oversells itself is worse than no tool:
HEIC conversion depends on your browser. It works where the browser can natively decode HEIC — Safari on macOS/iOS, or Windows with the HEIF extension installed. On most Linux setups it won't, and I'm not going to pretend otherwise.
Compression is browser-grade, not server-grade. It is genuinely useful for photos before you email or upload them, but a dedicated server encoder with more CPU time will still squeeze out a few more percent.
Analytics exists. There's page-level GA4 so I know which tools people actually open. Your input, your images and your text are never part of it, and there is no account system to attach them to.
How you'd use it
Open the tool you need — the tools index lists everything, or press Ctrl/Cmd + K anywhere to search.
Paste your text or drop your file. Results appear as you go. (The JSON tools also take Ctrl/Cmd + Enter to run.)
Copy the result or download it. Nothing is stored, so if you close the tab and come back, you start clean.
If you want to confirm the "no upload" claim yourself, the two-minute check: open DevTools → Network, filter on fetch/XHR, then run a tool with a large input. Nothing should leave the page. Or flip the Network panel to "Offline" — a locally-running tool keeps working.
Where it lives
https://tools.mindutil.com/ — 32 tools, 7 languages (English, 简体中文, 日本語, Deutsch, Español, Français, Português), free without an account.
If you only try one thing, try the JSON formatter on a minified API response you can't read. That's the case it exists for.