diff --git a/nip57.test.js b/nip57.test.js
new file mode 100644
index 0000000..6acc084
--- /dev/null
+++ b/nip57.test.js
@@ -0,0 +1,335 @@
+const {bech32} = require('@scure/base')
+const {
+  nip57,
+  generatePrivateKey,
+  getPublicKey,
+  finishEvent
+} = require('./lib/nostr.cjs')
+
+describe('getZapEndpoint', () => {
+  test('returns null if neither lud06 nor lud16 is present', async () => {
+    const metadata = {content: '{}'}
+    const result = await nip57.getZapEndpoint(metadata)
+
+    expect(result).toBeNull()
+  })
+
+  test('returns null if fetch fails', async () => {
+    const fetchImplementation = jest.fn(() => Promise.reject(new Error()))
+    nip57.useFetchImplementation(fetchImplementation)
+
+    const metadata = {content: '{"lud16": "name@domain"}'}
+    const result = await nip57.getZapEndpoint(metadata)
+
+    expect(result).toBeNull()
+    expect(fetchImplementation).toHaveBeenCalledWith(
+      'https://domain/.well-known/lnurlp/name'
+    )
+  })
+
+  test('returns null if the response does not allow Nostr payments', async () => {
+    const fetchImplementation = jest.fn(() =>
+      Promise.resolve({json: () => ({allowsNostr: false})})
+    )
+    nip57.useFetchImplementation(fetchImplementation)
+
+    const metadata = {content: '{"lud16": "name@domain"}'}
+    const result = await nip57.getZapEndpoint(metadata)
+
+    expect(result).toBeNull()
+    expect(fetchImplementation).toHaveBeenCalledWith(
+      'https://domain/.well-known/lnurlp/name'
+    )
+  })
+
+  test('returns the callback URL if the response allows Nostr payments', async () => {
+    const fetchImplementation = jest.fn(() =>
+      Promise.resolve({
+        json: () => ({
+          allowsNostr: true,
+          nostrPubkey: 'pubkey',
+          callback: 'callback'
+        })
+      })
+    )
+    nip57.useFetchImplementation(fetchImplementation)
+
+    const metadata = {content: '{"lud16": "name@domain"}'}
+    const result = await nip57.getZapEndpoint(metadata)
+
+    expect(result).toBe('callback')
+    expect(fetchImplementation).toHaveBeenCalledWith(
+      'https://domain/.well-known/lnurlp/name'
+    )
+  })
+})
+
+describe('makeZapRequest', () => {
+  test('throws an error if amount is not given', () => {
+    expect(() =>
+      nip57.makeZapRequest({
+        profile: 'profile',
+        event: null,
+        relays: [],
+        comment: ''
+      })
+    ).toThrow()
+  })
+
+  test('throws an error if profile is not given', () => {
+    expect(() =>
+      nip57.makeZapRequest({
+        event: null,
+        amount: 100,
+        relays: [],
+        comment: ''
+      })
+    ).toThrow()
+  })
+
+  test('returns a valid Zap request', () => {
+    const result = nip57.makeZapRequest({
+      profile: 'profile',
+      event: 'event',
+      amount: 100,
+      relays: ['relay1', 'relay2'],
+      comment: 'comment'
+    })
+    expect(result.kind).toBe(9734)
+    expect(result.created_at).toBeCloseTo(Date.now() / 1000, 0)
+    expect(result.content).toBe('comment')
+    expect(result.tags).toEqual(
+      expect.arrayContaining([
+        ['p', 'profile'],
+        ['amount', '100'],
+        ['relays', 'relay1', 'relay2']
+      ])
+    )
+    expect(result.tags).toContainEqual(['e', 'event'])
+  })
+})
+
+describe('validateZapRequest', () => {
+  test('returns an error message for invalid JSON', () => {
+    expect(nip57.validateZapRequest('invalid JSON')).toBe(
+      'Invalid zap request JSON.'
+    )
+  })
+
+  test('returns an error message if the Zap request is not a valid Nostr event', () => {
+    const zapRequest = {
+      kind: 1234,
+      created_at: Date.now() / 1000,
+      content: 'content',
+      tags: [
+        ['p', 'profile'],
+        ['amount', '100'],
+        ['relays', 'relay1', 'relay2']
+      ]
+    }
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      'Zap request is not a valid Nostr event.'
+    )
+  })
+
+  test('returns an error message if the signature on the Zap request is invalid', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = {
+      pubkey: publicKey,
+      kind: 9734,
+      created_at: Date.now() / 1000,
+      content: 'content',
+      tags: [
+        ['p', publicKey],
+        ['amount', '100'],
+        ['relays', 'relay1', 'relay2']
+      ]
+    }
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      'Invalid signature on zap request.'
+    )
+  })
+
+  test('returns an error message if the Zap request does not have a "p" tag', () => {
+    const privateKey = generatePrivateKey()
+
+    const zapRequest = finishEvent(
+      {
+        kind: 9734,
+        created_at: Date.now() / 1000,
+        content: 'content',
+        tags: [
+          ['amount', '100'],
+          ['relays', 'relay1', 'relay2']
+        ]
+      },
+      privateKey
+    )
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      "Zap request doesn't have a 'p' tag."
+    )
+  })
+
+  test('returns an error message if the "p" tag on the Zap request is not valid hex', () => {
+    const privateKey = generatePrivateKey()
+
+    const zapRequest = finishEvent(
+      {
+        kind: 9734,
+        created_at: Date.now() / 1000,
+        content: 'content',
+        tags: [
+          ['p', 'invalid hex'],
+          ['amount', '100'],
+          ['relays', 'relay1', 'relay2']
+        ]
+      },
+      privateKey
+    )
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      "Zap request 'p' tag is not valid hex."
+    )
+  })
+
+  test('returns an error message if the "e" tag on the Zap request is not valid hex', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = finishEvent(
+      {
+        kind: 9734,
+        created_at: Date.now() / 1000,
+        content: 'content',
+        tags: [
+          ['p', publicKey],
+          ['e', 'invalid hex'],
+          ['amount', '100'],
+          ['relays', 'relay1', 'relay2']
+        ]
+      },
+      privateKey
+    )
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      "Zap request 'e' tag is not valid hex."
+    )
+  })
+
+  test('returns an error message if the Zap request does not have a relays tag', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = finishEvent(
+      {
+        kind: 9734,
+        created_at: Date.now() / 1000,
+        content: 'content',
+        tags: [
+          ['p', publicKey],
+          ['amount', '100']
+        ]
+      },
+      privateKey
+    )
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBe(
+      "Zap request doesn't have a 'relays' tag."
+    )
+  })
+
+  test('returns null for a valid Zap request', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = finishEvent(
+      {
+        kind: 9734,
+        created_at: Date.now() / 1000,
+        content: 'content',
+        tags: [
+          ['p', publicKey],
+          ['amount', '100'],
+          ['relays', 'relay1', 'relay2']
+        ]
+      },
+      privateKey
+    )
+
+    expect(nip57.validateZapRequest(JSON.stringify(zapRequest))).toBeNull()
+  })
+})
+
+describe('makeZapReceipt', () => {
+  test('returns a valid Zap receipt with a preimage', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = JSON.stringify(
+      finishEvent(
+        {
+          kind: 9734,
+          created_at: Date.now() / 1000,
+          content: 'content',
+          tags: [
+            ['p', publicKey],
+            ['amount', '100'],
+            ['relays', 'relay1', 'relay2']
+          ]
+        },
+        privateKey
+      )
+    )
+    const preimage = 'preimage'
+    const bolt11 = 'bolt11'
+    const paidAt = new Date()
+
+    const result = nip57.makeZapReceipt({zapRequest, preimage, bolt11, paidAt})
+
+    expect(result.kind).toBe(9735)
+    expect(result.created_at).toBeCloseTo(paidAt.getTime() / 1000, 0)
+    expect(result.content).toBe('')
+    expect(result.tags).toContainEqual(['bolt11', bolt11])
+    expect(result.tags).toContainEqual(['description', zapRequest])
+    expect(result.tags).toContainEqual(['p', publicKey])
+    expect(result.tags).toContainEqual(['preimage', preimage])
+  })
+
+  test('returns a valid Zap receipt without a preimage', () => {
+    const privateKey = generatePrivateKey()
+    const publicKey = getPublicKey(privateKey)
+
+    const zapRequest = JSON.stringify(
+      finishEvent(
+        {
+          kind: 9734,
+          created_at: Date.now() / 1000,
+          content: 'content',
+          tags: [
+            ['p', publicKey],
+            ['amount', '100'],
+            ['relays', 'relay1', 'relay2']
+          ]
+        },
+        privateKey
+      )
+    )
+    const bolt11 = 'bolt11'
+    const paidAt = new Date()
+
+    const result = nip57.makeZapReceipt({zapRequest, bolt11, paidAt})
+
+    expect(result.kind).toBe(9735)
+    expect(result.created_at).toBeCloseTo(paidAt.getTime() / 1000, 0)
+    expect(result.content).toBe('')
+    expect(result.tags).toContainEqual(['bolt11', bolt11])
+    expect(result.tags).toContainEqual(['description', zapRequest])
+    expect(result.tags).toContainEqual(['p', publicKey])
+    expect(result.tags).not.toContain('preimage')
+  })
+})