Numeral base
Rewrite a number in another base, anywhere from binary up to base 36.
What is loaded above
Base 10 in, base 16 out, uppercase digits on. 3735928559 and 3405691582 are the decimal spellings of DEADBEEF and CAFEBABE. The first is a fill pattern written over memory so a read of something stale shows up in a dump. The second is the first four bytes of every Java class file. Each was picked because it spells a word in hex, and each is unrecognizable the moment it is written in decimal.
The difference from hex
Numeral base reads the input as a number and writes the same number in another notation. Hexadecimal reads the input as bytes.
Convert the decimal number 255 to base 16 here and it comes back as FF. Hex-encode the text 255 and you get 32 35 35, the three characters 2, 5 and 5. Same keystrokes, different question, and the wrong choice returns something that looks entirely plausible.
Bases, digits and precision
Bases run from 2 to 36 because the digits run out: 0 to 9, then a to z. Conversion is done in BigInt, so a 64-digit SHA-256 hash goes from base 16 to base 10 with every digit intact. Anything routed through a double would start lying above 2^53.
Input digits are read in either case, and the uppercase toggle applies to the output alone. Running the stage backwards swaps the two bases, so one pair of settings covers both directions.
What it will not do
Leading zeros are gone: 007 comes back as 7, because 7 is the value and the value is all that was read. Fractions are refused outright, and 3.14 raises "." is not a digit in base 10 rather than quietly truncating to 3.
Tokens split on whitespace and commas, convert one at a time, and rejoin with single spaces. A column pasted out of a spreadsheet converts in one pass and returns as a single line. A leading minus sign survives.
Related
Decimal bytes does the byte-oriented job this one is often mistaken for, giving 0 to 255 per byte. Binary is the same base-2 view applied to data rather than to a value.