Developer Tools
Fast, offline-capable utilities for encoding, parsing, debugging, and generating. 20 tools, zero ads in the tool itself, no data leaves your browser.
Most developer utility sites make you wait for three trackers to load before you can decode a JWT or format a blob of JSON. These do not. Every tool here runs client-side in your browser, which means your payload never touches our server. If you’re pasting in a production API key to inspect it, that is an important property.
Bookmark the ones you use. They work offline after first load.
Encoding and data formats
The daily glue code. JSON formatting, Base64 round-trips, URL percent-encoding, hashes for integrity checks, and regex testing. Every one of these is five clicks away from an IDE plugin, but two clicks away from here.
- JSON Formatter — prettify, minify, and validate any JSON blob
- Base64 Encoder / Decoder — text and binary-safe Base64 with URL-safe variant
- URL Encoder / Decoder — percent-encoding for query strings, form data, and HTML entities
- Hash Generator — MD5, SHA-1, SHA-256, SHA-512 on any input
- Regex Tester — live pattern matching with capture group highlighting
Tokens, timestamps, and formats
Debugging authentication and scheduled jobs usually means staring at a JWT or a cron expression until it makes sense. These tools make it make sense faster.
- JWT Decoder — inspect header, payload, and signature without sending anywhere
- Unix Timestamp Converter — epoch to human-readable in any timezone
- Cron Expression Generator — visual builder plus next-run-time preview
- .env File Validator — syntax check with common-mistake warnings
- Password Strength Checker — entropy estimate and crack-time projection
Web and design
Frontend work constantly needs color conversion, gradient code, favicons in eight sizes, images compressed without quality loss, and meta tags that preview correctly on every platform. These five cover the everyday cases.
- Color Converter — HEX, RGB, HSL, and HSV round-trips
- CSS Gradient Generator — linear, radial, and conic with copy-ready CSS
- Favicon Generator — all required sizes from a single upload
- Image Compressor — JPEG, PNG, and WebP with quality-vs-size preview
- Meta Tag Generator — Open Graph, Twitter Card, and SEO tags in one output
Generators and network utilities
The utilities that don’t quite fit elsewhere but you reach for often: strong passwords, QR codes for anything printable, subnet math that isn’t worth memorizing, and the YouTube thumbnail grab that always seems to come up for blog posts.
- Password Generator — configurable length, character sets, and entropy
- QR Code Generator — URLs, text, or vCards with downloadable PNG
- IP Subnet Calculator — CIDR math with network, broadcast, and host ranges
- YouTube Thumbnail Downloader — all four resolutions from any video URL
Every tool on this page runs entirely in your browser. Nothing you paste or type in gets sent to CalcMojo servers. Open devtools and check the network tab if you want to confirm.