Computer science
Computer science calculators
Number bases and Boolean algebra: the two foundations everything else in a computing course rests on.
Which calculation you need
Base conversion translates the same value into the four notations a machine and a programmer use: binary because circuits tell two states apart, hexadecimal because each of its digits is exactly four bits and makes a byte readable in two characters, octal for historical reasons that survive in file permissions. The same tool shows two's complement, the way negative numbers are held in memory and the reason the signed range is not symmetric. Boolean algebra builds the truth table of a logical expression, identifies tautologies and contradictions, and accepts the three notations textbooks use interchangeably: the words AND, OR and NOT, the symbols of logical product and sum, and the operators of programming languages.
Number base converter
Binary, octal, decimal and hexadecimal, with two's complement in 8, 16 and 32 bits.
Boolean algebra
Truth table of a logical expression, with tautologies and contradictions identified.
Base64 converter
From text, integer, hexadecimal or binary to Base64 and back, with the 6-bit groups explained.
IPv4 subnet calculator
Network, broadcast, usable hosts and masks from an IPv4 address with a CIDR prefix.
Hash generator
MD5, SHA-1, SHA-256, SHA-384 and SHA-512 of a text or of bytes, with a hash checker.
Unix timestamp converter
From Unix timestamp to date and time and back: seconds, milliseconds, UTC and local time.
Data size and download time
From bytes to gigabytes and gibibytes, and how long a file takes to download at a given speed.
Bitwise operations
AND, OR, XOR, NOT, shifts and rotations on 8, 16, 32 or 64-bit integers, with the bits on show.
IEEE 754 floating point
How a decimal is stored as a 32 or 64-bit float: sign, exponent, mantissa and the error.
Unicode and UTF-8 codes
The code point, UTF-8 and UTF-16 bytes and HTML code of every character, emoji included.
Colour converter
From HEX to RGB, HSL, HSV and CMYK and back, with the WCAG contrast of white and black text.
Password strength checker
Entropy in bits and time to guess it, with weak patterns recognised. Nothing leaves the browser.
URL encoder and decoder
Percent-encoding and decoding of values and addresses, and a URL taken apart into its pieces.
Regex tester
Test a regular expression on text: highlighted matches, capture groups and replacement, in JavaScript.
JSON formatter and validator
Format, minify and validate JSON: indentation, sorted keys and the exact position of errors.
Cron expression explainer
Turn a cron expression into words and see the next runs, field by field.
CRC32 and Adler-32 checksums
CRC-32, CRC-32C, four CRC-16 variants, CRC-8, Adler-32 and Fletcher-16 of text or hex bytes.
IPv6 subnet calculator
Network, address range, compressed and expanded forms, reverse DNS and splitting of an IPv6 prefix.