Revisiting BIP21

Revisiting BIP21

Original Postby MattCorallo

Posted on: March 1, 2024 17:16 UTC

The discussion revolves around the intricacies of updating BIP21, focusing on how to handle the prioritization of payment addresses when both off-chain and on-chain addresses are present with their own custom parameters.

A specific example given highlights the complexity: using a Bitcoin URI format that includes multiple addresses with different parameters, raising the question of how to indicate which address should take precedence without introducing order dependence at the URI level. This leads to the suggestion that perhaps the distinction between on-chain and off-chain addresses shouldn't exist, although backward compatibility necessitates some form of differentiation or ordering mechanism.

Further exploration into the subject touches upon the idea that the URI should encompass all acceptable payment instructions from the recipient's perspective, leaving the choice of payment method to the sender, who typically bears the transaction costs. This stance argues against distinguishing between on-chain and off-chain payment instructions within the payment protocol.

Additionally, the conversation notes that many existing implementations already assume or mandate the placement of certain instruction sets within the URI body, making significant alterations to this approach impractical. While there is a mention of potentially adding options for newer technologies like taproot/bech32m in the query parameters, the necessity and feasibility of such an inclusion are questioned.

The discourse also critiques the proposed 'addr' parameter, suggesting it lacks descriptive value compared to simply reusing the Human Readable Part (HRP), indicating a preference for maintaining clarity within the URI structure. To offer a structured solution to these considerations, a concrete set of changes has been proposed and documented in a pull request available at However, it’s acknowledged that these changes do not address the possibility of offering both Silent Payment instructions and Lightning options simultaneously, highlighting an area for further development.