There is no shortage of free developer tools. There is a shortage of free developer tools that are fast, that do not require an account, and that do not quietly upload your data.
These are the ones we actually use.
Text and encoding
JSON formatter — the one tool every developer needs daily. Most web-based versions upload your payload to a server. Ours does not.
Base64 encoder/decoder — needed constantly for data URLs, Basic auth headers and JWT segments. A browser extension or a two-line script is all you need.
Regex tester — a live match view with capture groups beats staring at a regex reference table every time.
Security
Password generator — critical distinction: whether it uses crypto.getRandomValues() or Math.random(). The second is predictable and should never protect a secret. Most online generators are honest about this, but not all.
Hash generator — SHA-256 for integrity checks and cache keys. Remember that fast hashes are the wrong choice for passwords; you want bcrypt, scrypt or Argon2 there.
JWT decoder — invaluable for debugging authentication issues. Decode locally so you never paste a live token into a third-party service.
Design
Colour converter — HEX, RGB, HSL, HSV and CMYK in one place, with a WCAG contrast ratio so you can check accessibility while you are there.
CSS unit converter — px to rem, with the reason to prefer rem for font sizes: it respects the user's font size preference.
Images
Image compressor — resizing removes more bytes than recompressing. A 4000px photo scaled to 1600px often drops 80% of the file size before quality settings are touched.
QR code generator — with the quiet zone and contrast rules that most generators leave you to guess.
The common thread
Notice the pattern: every tool above runs in the browser. That is not a technical preference, it is a property worth selecting for.
- It is faster — no round trip.
- It is private — the data never leaves.
- It is free — no compute cost to pass on.
A test for any tool you find
Before adding an online utility to your workflow, open the browser's Network tab and run it. If your data leaves the device, decide whether it needs to. Usually the answer for a formatter is no.
When it does need to — a PDF parser, an AI summariser, anything genuinely heavy — at least you now know which server to trust with it.