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nostr-expert

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SKILL.md

Nostr Protocol Expert (Quartz Implementation)

Practical patterns for working with Nostr in Quartz, AmethystMultiplatform's KMP Nostr library.

When to Use This Skill

  • Implementing Nostr event types (TextNote, Reaction, Zap, etc.)
  • Creating/parsing events with TagArrayBuilder DSL
  • Working with event kinds and tags
  • Finding NIP implementations in quartz/ codebase
  • Nostr cryptography (secp256k1 signing, NIP-44 encryption)
  • Bech32 encoding/decoding (npub, nsec, note formats)
  • Event validation and verification

For NIP specifications → Use nostr-protocol agent For Quartz implementation → Use this skill

Quartz Architecture

Quartz organizes code by NIP number:

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/
├── nip01Core/           # Core protocol (Event, Kind, Tags)
├── nip04Dm/             # Legacy DMs (deprecated)
├── nip10Notes/          # Text notes with threading
├── nip17Dm/             # Private DMs (gift wrap)
├── nip19Bech32/         # Bech32 encoding
├── nip44Encryption/     # Modern encryption (ChaCha20)
├── nip57Zaps/           # Lightning zaps
├── ... (57 NIPs total)
└── experimental/        # Draft NIPs

Pattern: nip##<Name>/ directories contain event classes, tags, and utilities for that NIP.

Find implementations: Use scripts/nip-lookup.sh <nip-number> or see references/nip-catalog.md.

Event Anatomy

Core Structure

kotlin
@Immutable
open class Event(
    val id: HexKey,              // SHA-256 hash of serialized event
    val pubKey: HexKey,          // Author's public key (32 bytes hex)
    val createdAt: Long,         // Unix timestamp
    val kind: Kind,              // Event kind (Int typealias)
    val tags: TagArray,          // Array of tag arrays
    val content: String,         // Event content
    val sig: HexKey,             // Schnorr signature (64 bytes hex)
) : IEvent

Key insight: Event is the base class. Specific event types (TextNoteEvent, ReactionEvent) extend it and add parsing/helper methods.

Kind Classification

kotlin
typealias Kind = Int

fun Kind.isEphemeral() = this in 20000..29999      // Not stored
fun Kind.isReplaceable() = this == 0 || this == 3 || this in 10000..19999
fun Kind.isAddressable() = this in 30000..39999    // Replaceable + has d-tag
fun Kind.isRegular() = this in 1000..9999          // Stored, not replaced

Pattern: Kind determines event lifecycle and replaceability.

Creating Events

EventTemplate Pattern

kotlin
fun eventTemplate(
    kind: Kind,
    content: String,
    tags: TagArray = emptyArray()
): EventTemplate

Usage:

kotlin
val template = eventTemplate(
    kind = 1,  // Text note
    content = "Hello Nostr!",
    tags = tagArray {
        add(arrayOf("subject", "Greeting"))
    }
)

// Sign with a signer
val signedEvent = signer.sign(template)

Why templates? Separates event data from signing. Templates can be signed by different signers (local keys, remote signers, hardware wallets).

TagArrayBuilder DSL

kotlin
fun <T : Event> tagArray(
    initializer: TagArrayBuilder<T>.() -> Unit
): TagArray

Methods:

  • add(tag) - Append tag
  • addFirst(tag) - Prepend tag (for ordering)
  • addUnique(tag) - Replace all tags with this name
  • remove(tagName) - Remove by name
  • addAll(tags) - Bulk add

Example:

kotlin
val tags = tagArray<TextNoteEvent> {
    add(arrayOf("e", replyToEventId, "", "reply"))
    add(arrayOf("p", authorPubkey))
    addUnique(arrayOf("subject", "Re: Hello"))
    add(arrayOf("content-warning", "spoilers"))
}

Pattern: Fluent DSL for building tag arrays with validation and deduplication.

Common Event Types

TextNoteEvent (kind 1)

kotlin
class TextNoteEvent : BaseThreadedEvent

Creating:

kotlin
val note = eventTemplate(
    kind = 1,
    content = "Hello world!",
    tags = tagArray {
        add(arrayOf("subject", "First post"))
    }
)

Parsing:

kotlin
val event: TextNoteEvent = ...
val subject = event.subject()  // Extension from nip14Subject
val mentions = event.mentions()  // List of p-tags
val quotedEvents = event.quotes()  // List of q-tags

ReactionEvent (kind 7)

kotlin
fun createReaction(
    targetEvent: Event,
    emoji: String = "+"
): EventTemplate {
    return eventTemplate(
        kind = 7,
        content = emoji,
        tags = tagArray {
            add(arrayOf("e", targetEvent.id))
            add(arrayOf("p", targetEvent.pubKey))
        }
    )
}

MetadataEvent (kind 0)

kotlin
data class UserMetadata(
    val name: String?,
    val displayName: String?,
    val picture: String?,
    val banner: String?,
    val about: String?,
    // ... more fields
)

fun createMetadata(metadata: UserMetadata): EventTemplate {
    return eventTemplate(
        kind = 0,
        content = metadata.toJson()  // Serialize to JSON
    )
}

Addressable Events (kinds 30000-40000)

kotlin
fun createArticle(
    slug: String,
    title: String,
    content: String
): EventTemplate {
    return eventTemplate(
        kind = 30023,
        content = content,
        tags = tagArray {
            addUnique(arrayOf("d", slug))  // Unique identifier
            add(arrayOf("title", title))
            add(arrayOf("published_at", "${TimeUtils.now()}"))
        }
    )
}

Key: d-tag makes it addressable. Events with same kind + pubkey + d-tag replace each other.

Tag Patterns

Tags are Array<String> with pattern [name, value, ...optionalParams].

Core Tags

e-tag (event reference):

kotlin
add(arrayOf("e", eventId, relayHint, marker))
// marker: "reply", "root", "mention"

p-tag (pubkey reference):

kotlin
add(arrayOf("p", pubkey, relayHint))

a-tag (addressable event):

kotlin
add(arrayOf("a", "$kind:$pubkey:$dtag", relayHint))

d-tag (identifier for addressable events):

kotlin
addUnique(arrayOf("d", "unique-slug"))

Tag Extensions

kotlin
// Find tags
event.tags.tagValue("subject")  // First subject tag value
event.tags.allTags("p")  // All p-tags
event.tags.tagValues("e")  // All e-tag values

// Parse structured tags
event.tags.mapNotNull(ETag::parse)  // Parse as ETag objects

For comprehensive tag patterns, see references/tag-patterns.md.

Threading (NIP-10)

kotlin
fun createReply(
    original: TextNoteEvent,
    content: String
): EventTemplate {
    return eventTemplate(
        kind = 1,
        content = content,
        tags = tagArray {
            // Reply marker
            add(arrayOf("e", original.id, "", "reply"))

            // Root marker (original's root, or original itself)
            original.rootEvent()?.let {
                add(arrayOf("e", it.id, "", "root"))
            } ?: add(arrayOf("e", original.id, "", "root"))

            // Tag author
            add(arrayOf("p", original.pubKey))

            // Tag all mentioned users
            original.mentions().forEach {
                add(arrayOf("p", it))
            }
        }
    )
}

Pattern: reply and root markers establish thread hierarchy.

Cryptography

Signing (secp256k1)

kotlin
interface ISigner {
    suspend fun sign(template: EventTemplate): Event
}

// Local key signing
class LocalSigner(private val privateKey: ByteArray) : ISigner {
    override suspend fun sign(template: EventTemplate): Event {
        val id = template.generateId()
        val sig = Secp256k1.sign(id, privateKey)
        return Event(id, pubKey, createdAt, kind, tags, content, sig)
    }
}

Pattern: Signers abstract key management. Can be local, remote (NIP-46), or hardware.

Encryption (NIP-44)

kotlin
// Modern encryption (ChaCha20-Poly1305)
object Nip44v2 {
    fun encrypt(plaintext: String, privateKey: ByteArray, pubKey: HexKey): String
    fun decrypt(ciphertext: String, privateKey: ByteArray, pubKey: HexKey): String
}

// Usage
val encrypted = Nip44v2.encrypt(
    plaintext = "Secret message",
    privateKey = myPrivateKey,
    pubKey = recipientPubKey
)

val decrypted = Nip44v2.decrypt(
    ciphertext = encrypted,
    privateKey = myPrivateKey,
    pubKey = senderPubKey
)

Pattern: Elliptic curve Diffie-Hellman + ChaCha20-Poly1305 AEAD.

NIP-04 (Deprecated)

kotlin
// Legacy encryption (NIP-04, deprecated for NIP-44)
object Nip04 {
    fun encrypt(msg: String, privateKey: ByteArray, pubKey: HexKey): String
    fun decrypt(msg: String, privateKey: ByteArray, pubKey: HexKey): String
}

Note: Use NIP-44 (Nip44v2) for new implementations. NIP-04 has security issues.

Bech32 Encoding (NIP-19)

kotlin
object Nip19 {
    // Encode
    fun npubEncode(pubkey: HexKey): String  // npub1...
    fun nsecEncode(privateKey: ByteArray): String  // nsec1...
    fun noteEncode(eventId: HexKey): String  // note1...
    fun neventEncode(eventId: HexKey, relays: List<String> = emptyList()): String
    fun nprofileEncode(pubkey: HexKey, relays: List<String> = emptyList()): String
    fun naddrEncode(kind: Int, pubkey: HexKey, dTag: String, relays: List<String> = emptyList()): String

    // Decode
    fun decode(bech32: String): Nip19Result
}

sealed class Nip19Result {
    data class NPub(val hex: HexKey) : Nip19Result()
    data class NSec(val hex: HexKey) : Nip19Result()
    data class Note(val hex: HexKey) : Nip19Result()
    data class NEvent(val hex: HexKey, val relays: List<String>) : Nip19Result()
    data class NProfile(val hex: HexKey, val relays: List<String>) : Nip19Result()
    data class NAddr(val kind: Int, val pubkey: HexKey, val dTag: String, val relays: List<String>) : Nip19Result()
}

Usage:

kotlin
// Encode
val npub = Nip19.npubEncode(pubkeyHex)
// Output: "npub1..."

// Decode
when (val result = Nip19.decode(npub)) {
    is Nip19Result.NPub -> println("Pubkey: ${result.hex}")
    is Nip19Result.NEvent -> println("Event: ${result.hex}, relays: ${result.relays}")
    else -> println("Other type")
}

Event Validation

kotlin
fun Event.verify(): Boolean {
    // 1. Verify ID matches content hash
    val computedId = generateId()
    if (id != computedId) return false

    // 2. Verify signature
    return Secp256k1.verify(id, sig, pubKey)
}

fun Event.generateId(): HexKey {
    val serialized = serializeForId()  // JSON array format
    return sha256(serialized)
}

Pattern: Always verify events from untrusted sources (relays).

Common Workflows

Publishing an Event

kotlin
suspend fun publishNote(content: String, signer: ISigner, relays: List<String>) {
    // 1. Create template
    val template = eventTemplate(kind = 1, content = content)

    // 2. Sign
    val event = signer.sign(template)

    // 3. Verify (optional but recommended)
    require(event.verify()) { "Signature verification failed" }

    // 4. Publish to relays
    relays.forEach { relay ->
        relayClient.send(relay, event)
    }
}

Querying Events

kotlin
// Subscription filter
data class Filter(
    val ids: List<HexKey>? = null,
    val authors: List<HexKey>? = null,
    val kinds: List<Kind>? = null,
    val since: Long? = null,
    val until: Long? = null,
    val limit: Int? = null,
    val tags: Map<String, List<String>>? = null  // e.g., {"#e": [eventId], "#p": [pubkey]}
)

// Usage
val filter = Filter(
    authors = listOf(userPubkey),
    kinds = listOf(1),  // Text notes only
    limit = 50
)

relayClient.subscribe(relay, filter) { event ->
    // Handle incoming events
}

Creating a Zap (NIP-57)

kotlin
fun createZapRequest(
    targetEvent: Event,
    amountSats: Long,
    comment: String = ""
): EventTemplate {
    return eventTemplate(
        kind = 9734,  // Zap request
        content = comment,
        tags = tagArray {
            add(arrayOf("e", targetEvent.id))
            add(arrayOf("p", targetEvent.pubKey))
            add(arrayOf("amount", "${amountSats * 1000}"))  // millisats
            add(arrayOf("relays", "wss://relay1.com", "wss://relay2.com"))
        }
    )
}

Gift-Wrapped DMs (NIP-17)

kotlin
fun createGiftWrappedDM(
    recipientPubkey: HexKey,
    message: String,
    signer: ISigner
): Event {
    // 1. Create sealed gossip (kind 14)
    val sealedGossip = createSealedGossip(message, recipientPubkey, signer)

    // 2. Wrap in gift wrap (kind 1059)
    return createGiftWrap(sealedGossip, recipientPubkey, signer)
}

Pattern: Double encryption + random ephemeral keys for metadata protection.

Finding NIPs

Use the bundled script:

bash
# Find by NIP number
scripts/nip-lookup.sh 44

# Search by term
scripts/nip-lookup.sh encryption
scripts/nip-lookup.sh "gift wrap"

Or see references/nip-catalog.md for complete catalog.

Bundled Resources

  • references/nip-catalog.md - All 57 NIPs with package locations and key files
  • references/event-hierarchy.md - Event class hierarchy, kind classifications, common types
  • references/tag-patterns.md - Tag structure, TagArrayBuilder DSL, common tag types, parsing patterns
  • scripts/nip-lookup.sh - Find NIP implementations by number or search term

Quick Reference

Task Pattern Location
Create event eventTemplate(kind, content, tags) nip01Core/signers/
Build tags tagArray { add(...) } nip01Core/core/
Sign event signer.sign(template) nip01Core/signers/
Verify signature event.verify() nip01Core/core/
Encrypt (NIP-44) Nip44v2.encrypt(...) nip44Encryption/
Bech32 encode Nip19.npubEncode(...) nip19Bech32/
Find NIP scripts/nip-lookup.sh <number> -

Common Event Kinds

Kind Type NIP Package
0 Metadata 01 nip01Core/
1 Text note 01, 10 nip10Notes/
3 Contact list 02 nip02FollowList/
5 Deletion 09 nip09Deletions/
7 Reaction 25 nip25Reactions/
1059 Gift wrap 59 nip59Giftwrap/
9734 Zap request 57 nip57Zaps/
9735 Zap receipt 57 nip57Zaps/
10002 Relay list 65 nip65RelayList/
30023 Long-form content 23 nip23LongContent/

Related Skills

  • nostr-protocol - NIP specifications and protocol details
  • kotlin-expert - Kotlin patterns (@Immutable, sealed classes, DSLs)
  • kotlin-coroutines - Async patterns for relay communication
  • kotlin-multiplatform - KMP patterns, expect/actual in Quartz

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