Chmod Calculator

How Chmod Calculator works

Build octal and symbolic Unix permissions from checkboxes. Read, write and execute map to 4, 2 and 1 — the reason 755 is so common. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

Three roles, three permissions

Every file has permissions for owner, group and other, and each role can read (4), write (2) and execute (1). Adding the numbers per role produces the octal mode: read plus write is 6, read plus execute is 5, all three is 7.

So 755 means owner rwx, group r-x, other r-x — the standard for a directory or an executable.

The modes you actually need

644 for a regular file, 755 for a directory or script, 600 for a private key, 700 for a directory only you should enter. Those four cover almost everything.

Why 777 is a mistake

World-writable files on a web server let any compromised process modify them, which is how a small bug becomes a defacement. If something “only works with 777”, the real problem is ownership, not permissions.

Directories need execute to be enterable; that is why a directory with 644 is unusable even though the files inside are readable.

Good to know

• Works offline once loaded, including on flights and in locked-down networks.
• No file size limit beyond your device's own memory.
• Free to use, with no account and no usage counter.
• Results are produced locally, so they are not logged or shared with anyone.

Questions