Network and system decoders: CIDR, HTTP, cron, chmod and User-Agent
Network and system decoders translate the compact notations that infrastructure runs on — CIDR subnet masks, raw HTTP messages, cron schedules, Unix permission modes, MAC addresses and User-Agent strings — into explicit, human-readable values.
Network, System & Packets tools
TCP / UDP / ICMP Header Decoder
Decode transport-layer packet headers from hex.
IP Header & CIDR Decoder
Decode IP headers and expand CIDR subnet ranges.
DNS Record Decoder
Parse DNS wire messages and resource records.
HTTP Request / Response Decoder
Parse raw HTTP messages into structured headers and body.
BGP Attribute Decoder
Decode BGP path attributes from raw bytes.
PCAP / PCAPNG Parser
Inspect capture-file structure and packet records.
MAC Address (OUI) Decoder
Resolve a MAC address to its vendor and inspect its bits.
User-Agent Parser
Break a User-Agent down into browser, engine and OS.
Cron Expression Decoder
Translate a cron expression into plain English.
Chmod Permission Calculator
Convert octal or symbolic chmod modes into readable permissions.
Which decoder do I need?
- An IP range like 192.168.1.0/24
- IP Header & CIDR
- A crontab line like */15 * * * *
- Cron Expression
- A mode like 755, 0644 or -rwxr-xr-x
- Chmod Permission
- A raw HTTP request or response
- HTTP Request / Response
- A browser User-Agent header
- User-Agent
- A MAC address like 00:1A:2B:3C:4D:5E
- MAC Address (OUI)
About network, system & packets decoding
Sysadmin notation is dense on purpose. 10.0.0.0/22 is a range of 1,024 addresses, 0 */6 * * 1-5 is a schedule, 0755 is three sets of permissions, and a single User-Agent string encodes a browser, rendering engine, operating system and device. Each is quick to write and easy to misread, and a wrong guess means an open firewall rule, a job that never runs or a file nobody can execute.
These decoders spell each notation out field by field: the first and last host and broadcast address of a subnet, every header of an HTTP request, a cron schedule in plain English, permissions as rwx triplets, and the vendor prefix and flag bits of a MAC address. All of them run in your browser with nothing sent to a server.
Frequently asked questions
How many addresses are in a /24 subnet?
256 addresses, of which 254 are usable hosts on a traditional IPv4 network — the first is the network address and the last is the broadcast address. Each step down in prefix length doubles the size: a /23 has 512 and a /22 has 1,024.
What does chmod 755 mean?
The owner can read, write and execute (7 = 4+2+1); the group and everyone else can read and execute (5 = 4+1). It is the usual mode for directories and executable scripts.
What does */5 mean in a cron expression?
Every fifth value of that field. In the minute field, */5 runs at minutes 0, 5, 10 and so on — every five minutes.
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