TCP Header Decoder

Paste raw TCP header hex and decode ports, sequence/ack numbers, flags, and window size.

TCP header hex (≥ 20 bytes)

Source port12345

Destination port50104

Sequence305419896

Ack2596069109

Header length0 bytes

FlagsNS, CWR, PSH

Window8192

Checksum0xE730

Urgent0

How to read the result

Bytes 0–3 are source/destination ports, 4–11 are sequence and ack numbers, byte 13 holds the classic flags (SYN, ACK, FIN, RST, PSH...), bytes 14–15 are the window size.

Example

3039c3b8... → src 12345, dst 50040, flags SYN

FAQ

How many bytes do I need?

At least 20 bytes (40 hex chars). Longer headers include TCP options.

What do the flags mean?

SYN opens, ACK acknowledges, FIN closes, RST aborts, PSH pushes data now.