Seven Free Tools That Run Entirely in Your Browser
I keep reaching for little developer utilities — a password generator here, a JWT decoder there — and almost every one of them wants me to paste my data into someone else's server. For a checksum or a token that's usually harmless. For a secret, a private key, or a real password, it's exactly the wrong place to put it.
So I built my own, the same way I built the photo editor: everything runs locally in your browser. No sign-up, no backend, nothing uploaded. You can open one, do the job, and close the tab — your input was never anywhere but your own machine.
You'll find them all under the new Tools section. Here's what's live today.
What's in the box
- Password Generator — strong, random passwords with control over length, casing, numbers, and symbols, generated with the Web Crypto API.
- UUID Generator — random v4 UUIDs in bulk, with optional casing, hyphens, and braces.
- JSON Formatter & Validator — format, validate, minify, and sort JSON, with clear line-and-column error messages.
- JWT Decoder — inspect a token's header, payload, and claims with human-readable expiry. Decode-only, so it never asks for your secret.
- Token Counter & Cost Estimator — estimate the tokens in a prompt and what it'll cost across Claude and GPT models.
- Hash & Checksum — SHA-256/1/384/512 of text or files, with a built-in verify-against-a-known-hash check.
- Base64 Encoder & Decoder — UTF-8 safe encoding and decoding, with a URL-safe option.
Why local-only
The same reasoning as the photo editor. Keeping everything in the browser is simpler to reason about, it's genuinely private, and it means I'm not paying to shuttle anyone's data around. You get the tool; I don't get your data. For things like passwords, tokens, and private files, that isn't a nice-to-have — it's the whole point.
It's also a quietly nice fit for the kind of work I write about here: shipping small, useful things fast, without dragging a server and a database along for the ride.
Try them and tell me what's missing
More are on the way, and I'd rather build the ones people actually want. If there's a utility you reach for constantly — or one of these is missing an option you need — let me know.
Browse the tools: matssjodin.com/tools
Send feedback: matssjodin.com/contact