Developer Tools Calculators

Format, minify, validate and sort JSON entirely in your browser. Precise error messages with line and column, and nothing is ever uploaded.

Encode text to Base64 or decode it back, with URL-safe output and full Unicode support. Runs entirely in your browser.

Percent-encode text for URLs or decode it back, with the choice between full-URI and component encoding explained.

Generate SHA-256, SHA-1 and CRC32 hashes of any text in your browser, with guidance on which one is appropriate for what.

Generate cryptographically random version 4 UUIDs in bulk, with optional uppercase, braces or hyphen-free formatting.

Generate cryptographically random passwords with a chosen length and character set, plus an entropy estimate of how strong they actually are.

Roll any combination of dice — standard or custom-sided — with the total, each individual roll and the full probability distribution.

Convert Unix timestamps to human-readable UTC dates and back, handling both seconds and milliseconds.

Count words, characters, sentences and paragraphs, with reading time, keyword frequency and byte size.

Convert between Roman numerals and ordinary numbers in either direction, with every subtractive pair explained.

Convert any number between decimal, binary, hexadecimal and octal, with the place-value breakdown shown for each.

Calculate the network address, broadcast address, usable host range and host count for an IPv4 address and CIDR prefix.

Calculate how long a file transfer, download or backup will take, given a file size and connection speed.

Convert a colour between hex, RGB, HSL, HSV and CMYK, and check its WCAG contrast ratio against another colour.

Simplify pixel dimensions to their aspect ratio, or resize an image or video to a new width or height while keeping the proportions exact.

Work out a screen's real width and height from its diagonal and aspect ratio, with pixel density in PPI, dot pitch and viewing distance.

Translate a cron expression into plain English and list its next scheduled run times, with warnings for the day-of-week trap.

Convert between px, rem, em, pt, %, and physical CSS units, with the root and parent font sizes taken into account.

Generate placeholder text by paragraphs, sentences or words, with a fixed seed so the same settings always produce the same output.

Turn any title into a clean URL slug, with accented characters transliterated rather than stripped, and optional stop-word removal.