diff --git a/publish/src/core/event.ts b/publish/src/core/event.ts
new file mode 100644
index 0000000..6bdc595
--- /dev/null
+++ b/publish/src/core/event.ts
@@ -0,0 +1,43 @@
+import type { Frontmatter } from './frontmatter.ts'
+
+export interface UnsignedEvent {
+  kind: number
+  pubkey: string
+  created_at: number
+  tags: string[][]
+  content: string
+}
+
+export interface BuildArgs {
+  fm: Frontmatter
+  rewrittenBody: string
+  coverUrl: string | undefined
+  pubkeyHex: string
+  clientTag: string
+  nowSeconds: number
+  additionalTags?: string[][]
+}
+
+export function buildKind30023(args: BuildArgs): UnsignedEvent {
+  const { fm, rewrittenBody, coverUrl, pubkeyHex, clientTag, nowSeconds, additionalTags } = args
+  const publishedAt = Math.floor(fm.date.getTime() / 1000)
+  const tags: string[][] = [
+    ['d', fm.slug],
+    ['title', fm.title],
+    ['published_at', String(publishedAt)],
+  ]
+  if (fm.description) tags.push(['summary', fm.description])
+  if (coverUrl) tags.push(['image', coverUrl])
+  if (Array.isArray(fm.tags)) {
+    for (const t of fm.tags) tags.push(['t', String(t)])
+  }
+  if (clientTag) tags.push(['client', clientTag])
+  if (additionalTags) tags.push(...additionalTags)
+  return {
+    kind: 30023,
+    pubkey: pubkeyHex,
+    created_at: nowSeconds,
+    tags,
+    content: rewrittenBody,
+  }
+}
diff --git a/publish/tests/event_test.ts b/publish/tests/event_test.ts
new file mode 100644
index 0000000..3c2e637
--- /dev/null
+++ b/publish/tests/event_test.ts
@@ -0,0 +1,94 @@
+import { assertEquals } from '@std/assert'
+import { buildKind30023 } from '../src/core/event.ts'
+import type { Frontmatter } from '../src/core/frontmatter.ts'
+
+const PUBKEY = '4fa5d1c413e2b45e10d40bf3562ab701a5331206e359c90baae0e99bfd6c6e41'
+
+Deno.test('buildKind30023: minimaler Post liefert alle Pflicht-Tags', () => {
+  const fm: Frontmatter = {
+    title: 'Hello',
+    slug: 'hello',
+    date: new Date('2024-01-15T00:00:00Z'),
+  }
+  const ev = buildKind30023({
+    fm,
+    rewrittenBody: 'body text',
+    coverUrl: undefined,
+    pubkeyHex: PUBKEY,
+    clientTag: 'test-client',
+    nowSeconds: 1_700_000_000,
+  })
+  assertEquals(ev.kind, 30023)
+  assertEquals(ev.pubkey, PUBKEY)
+  assertEquals(ev.created_at, 1_700_000_000)
+  assertEquals(ev.content, 'body text')
+  const tags = ev.tags
+  assertEquals(tags.find((t) => t[0] === 'd'), ['d', 'hello'])
+  assertEquals(tags.find((t) => t[0] === 'title'), ['title', 'Hello'])
+  assertEquals(
+    tags.find((t) => t[0] === 'published_at')?.[1],
+    String(Math.floor(Date.UTC(2024, 0, 15) / 1000)),
+  )
+  assertEquals(tags.find((t) => t[0] === 'client'), ['client', 'test-client'])
+})
+
+Deno.test('buildKind30023: mapping summary / image / tags', () => {
+  const fm: Frontmatter = {
+    title: 'T',
+    slug: 's',
+    date: new Date('2024-01-01'),
+    description: 'Summary text',
+    tags: ['Foo', 'Bar Baz'],
+  }
+  const ev = buildKind30023({
+    fm,
+    rewrittenBody: 'b',
+    coverUrl: 'https://bl.example/cover-hash.png',
+    pubkeyHex: PUBKEY,
+    clientTag: 'x',
+    nowSeconds: 1,
+  })
+  assertEquals(ev.tags.find((t) => t[0] === 'summary'), ['summary', 'Summary text'])
+  assertEquals(
+    ev.tags.find((t) => t[0] === 'image'),
+    ['image', 'https://bl.example/cover-hash.png'],
+  )
+  assertEquals(
+    ev.tags.filter((t) => t[0] === 't'),
+    [['t', 'Foo'], ['t', 'Bar Baz']],
+  )
+})
+
+Deno.test('buildKind30023: ohne coverUrl kein image-tag', () => {
+  const fm: Frontmatter = {
+    title: 'T',
+    slug: 's',
+    date: new Date('2024-01-01'),
+  }
+  const ev = buildKind30023({
+    fm,
+    rewrittenBody: 'b',
+    coverUrl: undefined,
+    pubkeyHex: PUBKEY,
+    clientTag: 'x',
+    nowSeconds: 1,
+  })
+  assertEquals(ev.tags.some((t) => t[0] === 'image'), false)
+})
+
+Deno.test('buildKind30023: leerer clientTag wird weggelassen', () => {
+  const fm: Frontmatter = {
+    title: 'T',
+    slug: 's',
+    date: new Date('2024-01-01'),
+  }
+  const ev = buildKind30023({
+    fm,
+    rewrittenBody: 'b',
+    coverUrl: undefined,
+    pubkeyHex: PUBKEY,
+    clientTag: '',
+    nowSeconds: 1,
+  })
+  assertEquals(ev.tags.some((t) => t[0] === 'client'), false)
+})