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.
Why does my code print a file mode as 493?
Because 493 is the decimal value of the octal mode 755. Python, Go and others store the mode as a plain integer, so printing it without an octal format shows 493. Convert 493 here and you get 755 back, which is the number chmod expects.
What is 255 in octal?
377. That is the largest value a single byte can hold, expressed in three octal digits. The leading digit is capped at 3 because eight bits split into 2 + 3 + 3 when grouped in threes.
What is the largest three-digit octal number?
777, which is 511 in decimal. That is why file modes stop at 777: three digits, each covering a three-bit permission triad, gives a maximum of 9 bits.
Do I need to add a leading zero to the result?
Only if the target expects one. The C and older Python convention writes an octal literal as 0755, and modern Python uses 0o755. The chmod command takes 755 with no prefix at all, which is exactly what this tool prints.
Can it convert negative numbers?
Yes, but with a minus sign in front of the magnitude, so -8 becomes -10. It does not produce a two's complement representation, because that requires a fixed bit width the tool does not assume.