Does my data get uploaded anywhere?
No. Everything runs locally in your browser and nothing is sent to a server.
Is this free to use?
Yes. It is completely free, with no account, no signup, and no usage limits.
Does it work on a phone?
Yes. The page runs in any modern mobile browser, on iPhone and Android alike, with no app to install.
How many bits does one hex digit expand to?
Always four, which is why hex and binary map cleanly onto each other. Each digit is a nibble: 0 is 0000 up to f which is 1111. A two-digit hex byte is therefore exactly eight bits, with no ambiguity.
Why does 0f give 1111 instead of 00001111?
Because the tool converts a number, and a number carries no leading zeros. If you are laying out a byte, pad the output on the left to eight characters. Each hex digit still expands to four bits, and the padding is presentation only.
Does the case of the hex digits matter?
No. ff, FF and Ff all parse to the same value, and a 0x or 0X prefix is stripped before parsing. Hex has been case-insensitive since it was invented, and the tool follows that.
How do I convert a hex colour like 1E90FF into binary?
Split it into its three byte pairs first: 1E, 90 and FF. Convert them separately so each gives you eight bits (00011110, 10010000, 11111111). Pasting 1E90FF as one token converts it as a single 24-bit number instead, which loses the byte alignment.
Can I convert several hex bytes at once?
Yes. Separate them with spaces, commas, or new lines and each converts independently, keeping the order. That makes pasting the hex column of a dump straightforward, as long as you leave out the offsets.