LNURL

LNURL is a set of protocols that wrap Lightning interactions in ordinary HTTP requests, so wallets can fetch what they need instead of making users copy long strings.

Why it matters

Raw Lightning UX is hostile: invoices expire, are single-use, and are unreadable. LNURL puts a server in the middle that mints them on demand, which is the foundation of anything resembling a reusable payment identity.

The cost is a server. An invoice is a message between two nodes; an LNURL is a promise that a web endpoint will still answer tomorrow. The identity is only as durable as whoever runs that host.

How it works

The specifications are numbered LUDs. LUD-01 defines the base encoding — an HTTPS URL in bech32, which is the lnurl1… string a QR code carries. LUD-17 allows the raw URL with a scheme prefix instead, which is what most modern wallets use.

The subprotocols cover the common flows: LUD-06 for pay, LUD-03 for withdraw, LUD-04 for auth, LUD-02 for channel requests. In LUD-06 the wallet fetches the URL and receives a callback address, a minimum and maximum amount, and a metadata string that must contain a text/plain entry. The wallet then calls back with a chosen amount and receives an invoice whose description hash commits to that exact metadata, so the wallet can prove the invoice matches what it was shown.

LUD-09 adds a success message after payment, LUD-12 a comment field, and LUD-16 the static identifier behind a Lightning Address.

Related

• Lightning Address — LNURL-pay behind an email-shaped identifier

Sources

• https://github.com/lnurl/luds