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.
What is chmod 755 in hex?
1ED. The mode is 9 bits (111101101), which is 493 in decimal and 1ED in hex. You will see this form whenever a program formats a file mode with a hex specifier instead of an octal one.
Why does octal 777 need three hex digits?
Because 777 is nine bits, which is 511, and two hex digits only reach 255. Three hex digits cover 12 bits, so 777 becomes 1FF with the leading 1 carrying the ninth bit.
Is 8 a valid digit here?
No. Octal uses the digits 0 to 7 only, and the tool errors and names the character rather than guessing. If your input contains an 8 or a 9, it was almost certainly decimal, not octal.
Why is the hex output uppercase?
It is the usual convention for constants and masks, and hex is case-insensitive, so 1ED and 1ed carry the same value. Lowercase it after copying if your style guide wants that.
Can I paste a 0o prefix or a leading zero?
Yes. The 0o prefix is stripped and a plain leading zero has no value, so 0755, 0o755 and 755 all convert to 1ED.