Lightning Zaps (NIP-57)

Value-for-value payments on Nostr. Bitcoin Lightning integrated directly into the social protocol.

The Flow#

   SENDER                    LNURL PROVIDER            RECEIVER
┌──────────┐               ┌──────────────┐         ┌──────────┐
│  Alice   │               │   Wallet/    │         │   Bob    │
│          │──① fetch LN──▶│   LN node    │         │          │
│          │   URL          │              │         │          │
│          │◄──────────────│              │         │          │
│          │   callback URL │              │         │          │
│          │                │              │         │          │
│          │──② Zap Req────▶│              │         │          │
│  Kind    │   (kind 9734)  │              │         │          │
│  9734    │                │──③ pay──────▶│         │          │
│          │                │   invoice    │         │          │
│          │                │◄─────────────│         │          │
│          │                │   preimage   │         │          │
│          │                │              │         │          │
│   Kind   │                │──④ Zap Rcpt─▶│ relays  │──▶Bob    │
│   9735   │                │   (kind 9735)│◄────────│   sees   │
│          │                │              │          │   zap    │
└──────────┘               └──────────────┘         └──────────┘

Event Types#

Kind 9734 — Zap Request#

The payment intent. Sent to the LNURL-pay endpoint.

{
  "kind": 9734,
  "content": "",
  "tags": [
    ["relays", "wss://relay.damus.io", "wss://nos.lol"],
    ["amount", "21000"],
    ["lnurl", "lnurl1d..."],
    ["p", "<recipient-pubkey>"],
    ["e", "<optional-event-id>"],
    ["a", "<optional-addressable-event>"],
    ["P", "<optional-zapper-pubkey>"]
  ]
}

amount is in millisatoshis: 21000 = 21 sats.

Kind 9735 — Zap Receipt#

Published by the LNURL provider after payment succeeds. This is the public proof of payment.

{
  "kind": 9735,
  "pubkey": "<provider's pubkey>",
  "content": "",
  "tags": [
    ["p", "<recipient-pubkey>"],
    ["P", "<sender-pubkey>"],
    ["e", "<event-id>"],
    ["bolt11", "<invoice>"],
    ["description", "<JSON-encoded zap request>"],
    ["preimage", "<payment preimage>"]
  ]
}

Validation#

1. zap receipt pubkey MUST match the LNURL provider's nostrPubkey
2. invoiceAmount in bolt11 MUST equal amount tag in zap request
3. SHA256(description) MUST match bolt11 description hash

LNURL Provider Setup#

The recipient's Lightning node must expose:

GET /.well-known/lnurlp/<username>
→ {
    "callback": "https://ln.example.com/callback",
    "maxSendable": 100000000,
    "minSendable": 1000,
    "metadata": "[...]",
    "nostrPubkey": "<provider's nostr pubkey>",
    "allowsNostr": true,
    "tag": "payRequest"
  }

allowsNostr: true signals zap compatibility to clients.

Split Zaps#

Send to multiple recipients in one zap:

{
  "tags": [
    ["zap", "<pubkey1>", "wss://relay1.com", "1"],
    ["zap", "<pubkey2>", "wss://relay2.com", "1"],
    ["zap", "<pubkey3>", "wss://relay3.com", "2"]
  ]
}

Weight calculation: Bob gets 25%, Carol gets 25%, Dave gets 50%.

Without weights: equal split. Missing weight: that recipient gets 0.

Anonymous Zaps#

• No P tag in zap request = anonymous
• Recipient sees only that someone zapped, not who
• Provider still knows (payment is real), but recipient doesn't

Zap Goals (NIP-75)#

Crowdfunding targets on Nostr.

Kind 9041:

{
  "kind": 9041,
  "content": "Help me buy a new laptop!",
  "tags": [
    ["amount", "100000000"],      // target: 100k sats
    ["relays", "wss://..."],
    ["closed_at", "1700000000"]   // deadline
  ]
}

The sum of all zap receipts for this goal is compared against the target.

Fee Model#

Layer	Fee	Who Pays
LNURL provider	Configurable	Provider or sender
Lightning routing	Per-hop fees	Sender
On-chain (if needed)	Market rate	Whoever closes channel
Nostr relay	Free	N/A

Typical total: 0–2 sats for a 21 sat zap.

Why Zaps Beat Tips#

Aspect	Tip (Kind 1 reply)	Zap (Kind 9735)
Verifiable	❌ Trust-me-bro text	✅ Cryptographic proof
Amount visible	Only if claimed	✅ In bolt11 invoice
Sender visible	Only if claimed	✅ In zap receipt
LN address	Static	Dynamic callback
Split support	❌	✅ Weight-based
Anonymity	❌	✅ Omit P tag

Client Display#

Clients show zaps as:

⚡ Alice zapped 21 sats
⚡ Bob zapped 1000 sats to you
⚡ 3 people zapped 42 sats each

Sorting by total zapped amount is the defacto trending algorithm.

Implementation Notes#

Creating a Zap (Client-Side)#

// 1. Fetch LNURL from recipient's profile
const lnurl = await fetchLnurl(recipientPubkey)

// 2. Create Zap Request event
const zapRequest = await signEvent({
  kind: 9734,
  content: "",
  tags: [
    ["relays", ...relays],
    ["amount", sats * 1000],
    ["lnurl", lnurl],
    ["p", recipientPubkey],
  ]
})

// 3. Send to LNURL callback
const {pr: invoice} = await fetch(`${callback}?amount=${amount}&nostr=${encodeURI(JSON.stringify(zapRequest))}`)

// 4. Pay invoice
await payInvoice(invoice)

Verifying a Zap Receipt#

// 1. Get LNURL provider's nostrPubkey
const providerPubkey = await getProviderPubkey(lnurl)

// 2. Verify zap receipt pubkey matches provider
if (zapReceipt.pubkey !== providerPubkey) throw "Invalid provider"

// 3. Verify invoice amount matches request amount
if (decodeInvoice(zapReceipt.bolt11).amount !== zapRequest.amount) throw "Amount mismatch"

// 4. Verify description hash
if (sha256(zapReceipt.description) !== decodeInvoice(zapReceipt.bolt11).descriptionHash) throw "Hash mismatch"

Quick Reference#

What	Kind	Key Tags	Direction
Zap Request	9734	p, amount, lnurl, relays	Client → LNURL
Zap Receipt	9735	p, P, bolt11, description, preimage	LNURL → Relays
Zap Goal	9041	amount, relays, closed_at	User → Relays