Sysadmin Toolkit
2 essential sysadmin utilities in one tool: an IPv4 subnet/CIDR calculator (network, broadcast, mask, usable host range) and a bidirectional Linux chmod permission calculator (checkboxes ↔ octal ↔ symbolic notation).
- Pick a mode from the pill bar: IPv4 Subnet / CIDR Calculator or Linux chmod Calculator.
- For subnetting, type a CIDR block like 192.168.1.0/24 and instantly see network address, broadcast, mask, wildcard mask, usable host range, and address counts.
- For chmod, either check the Read/Write/Execute boxes for Owner, Group, and Other, or type an octal value like 755 or a symbolic string like rwxr-xr-x directly — both stay in sync.
- Set a filename to see the full chmod command, then copy it straight into your terminal.
All processing happens entirely in your browser. Your data never leaves your device.
Key Features
- CIDR calculator computes network address, broadcast, subnet mask, and wildcard mask
- Shows first/last usable host and total vs. usable address counts
- Correctly handles /31 point-to-point (RFC 3021) and /32 host-route special cases
- chmod calculator with checkbox groups for Owner, Group, and Other permissions
- Bidirectional chmod input — type an octal value or symbolic string and the checkboxes sync automatically
- Live octal and symbolic permission string output
- Copyable chmod command with a customizable filename
- 100% client-side — no networking data or filenames ever leave your device
About Sysadmin Toolkit
Two calculations come up constantly for anyone who touches servers, networking configs, or a Linux shell: figuring out the usable address range of a subnet, and working out the right permission bits for a file or directory. Both are simple bit arithmetic, but easy to get wrong under time pressure — miscounting a subnet's broadcast address or mixing up which digit is owner vs. group in chmod 750 are classic mistakes.
The IPv4 Subnet / CIDR Calculator takes standard CIDR notation (e.g. 10.0.0.0/16) and hand-computes every value a network engineer needs: the network and broadcast addresses, the subnet mask and its wildcard-mask complement (used in ACLs), the first and last usable host, and the total vs. usable address counts. It correctly special-cases the two smallest useful blocks — /31 point-to-point links (RFC 3021, both addresses usable, no network/broadcast reservation) and /32 host routes (a single usable address).
The Linux chmod Calculator works the other direction: three checkbox groups for Owner, Group, and Other (each with Read/Write/Execute) compute the octal permission (e.g. 755) and symbolic string (rwxr-xr-x) live, and it's fully bidirectional — type 750 or rwxr-x--- directly into the text field and the checkboxes update to match. A ready-to-copy chmod 755 filename command is generated so you can paste straight into a terminal.
Frequently Asked Questions
In a standard subnet, the network address (the lowest address in the block) identifies the subnet itself and can't be assigned to a device, so the first usable host is one address higher. The broadcast address (the highest address) is similarly reserved, so the last usable host is one address lower — except in /31 and /32 blocks, which don't reserve these.
A /32 has only one address total, so it's used as a single host route with that one address as both 'network' and the usable host. A /31 has exactly two addresses; RFC 3021 defines both as usable for point-to-point links (e.g. router-to-router) rather than reserving one for a broadcast address.
Each digit is the sum of Read (4), Write (2), and Execute (1) for one group, in order: Owner, Group, Other. 750 means Owner has read+write+execute (7), Group has read+write (5), and Other has no access (0).
Yes — the text field accepts either a 3-digit octal value (755) or a 9-character symbolic string (rwxr-xr-x, with or without a leading file-type character like the - or d you'd see in ls -l output), and the checkboxes update to match either format.
No. Both calculators run entirely as JavaScript in your browser tab — the CIDR block, filenames, and permission settings you enter are never transmitted or logged.