How to verify if it's Segwit Transaction or not?

Question

Segwit Usage chart example : https://p2sh.info/dashboard/db/segwit-usage?orgId=1

I Would like to verify by checking tx if it's Segwit Transaction or not.

Is there any simple method to do this?

• legacy -> P2SH tx (Is this Segwit Transaction?)
• P2SH -> legacy tx (Is this Segwit Transaction?)
• bech32 -> legacy tx (Is this Segwit Transaction?)

What about when many types of addresses are set as inputs and outputs?

Answer 1

A transaction is a segwit tx if at least one of the inputs contain a witness. Or if you are inspecting the raw tx then you check the 5th byte (the input count) and if it is 0x00 then it is a segwit tx.

Example: tx1

02000000055f4e5315ffe854e75db92f8dda952a8db2f63b37838fca4c32bd4bb692fe7ea2000000006a47304402200ab62a9d1858dceeaa2101cda3f31b7bae60471c0355c54a6eae48f723555806022010d2aad6362a8c56ed66b0670ff84175f534f4f0995f8724a9b2a5fc89a2a4b4012102c424c2670a7aade9cf867576064013d02cc7669c418968993e73e6b25fc122bcfeffffff80cb1bfcde0f309490c717eca07f1353f121fb13e105...

is not a segwit tx because the input count is 0x05 = 5

tx2

0100000000010106325bac2f2e7ca67fa46c8304fb3b747e5578df1eef0394349ce2cdd744f7f10100000000ffffffff02db355202000000001976a91489ea1263056ac068adba4844efb376a3a19635ad88ac43b72f07000000002...

is a segwit tx because the input count is 0x00 = 0

Also:

• Transactions spending P2PKH inputs (address starting with 1) cannot be segwit.
• Transactions spending P2SH inputs will be segwit if they are nested P2SH, otherwise not.
• Transactions spending P2WPKH or P2WSH (starting with bc1) will be segwit.

In your example:

legacy -> P2SH

This cannot be a segwit tx because it spends inputs from a legacy address

P2SH -> legacy

This can be a segwit tx if the address is P2SH-P2WPKH or P2SH-P2WSH (nested segwit into P2SH). You wouldn't know if it is nested if it's not your's unless someone has already spent from it (in which case you inspect the spending tx).

bech32 -> legacy

This is always a segwit tx