H3 — Address reuse on input

Severity: Critical · Weight: 20 · Network: Yes

What it detects

One or more input addresses have been used in previous transactions (i.e. they have a transaction history on-chain).

Why it matters

Bitcoin addresses are not meant to be reused. Each time you reuse an address, you link all transactions involving that address together — effectively creating a permanent public record connecting all your activity through that address.

Network requirement

H3 queries mempool.space (blockstream.info fallback) for the transaction history of each input address. It is skipped when lookup=False (the default).

What to do

• Generate a fresh address for every transaction
• Most modern HD wallets do this automatically — check your wallet settings
• If you reused an address, consider consolidating those UTXOs in a coinjoin before spending further

Privacy note

Running H3 sends each input address to an external block explorer. Use --rpc-url to route lookups through your own node, or disable it with lookup=False if you do not want address data leaving your machine.