diff --git a/src/components/PostHeader.astro b/src/components/PostHeader.astro
new file mode 100644
index 0000000..b939ec2
--- /dev/null
+++ b/src/components/PostHeader.astro
@@ -0,0 +1,88 @@
+---
+interface Props {
+  title: string;
+  date: Date;
+  type?: string;
+  readingTime?: number;
+}
+
+const { title, date, type = 'post', readingTime } = Astro.props;
+
+const formattedDate = date.toLocaleDateString('en-US', {
+  year: 'numeric',
+  month: 'long',
+  day: 'numeric',
+});
+const isoDate = date.toISOString().split('T')[0];
+---
+
+<header class="post-header">
+  <span class="badge">{type}</span>
+  <h1 class="title">{title}</h1>
+  <p class="meta">
+    <time datetime={isoDate}>{formattedDate}</time>{readingTime && ` · ${readingTime} min read`}
+  </p>
+</header>
+
+<style>
+  .post-header {
+    max-width: var(--width-prose);
+    margin-left: auto;
+    margin-right: auto;
+    padding-top: var(--space-8);
+    padding-bottom: var(--space-8);
+    text-align: center;
+  }
+
+  .badge {
+    font-family: var(--font-structure);
+    font-size: var(--type-xs);
+    font-weight: 600;
+    color: var(--accent-primary);
+    text-transform: uppercase;
+    letter-spacing: 0.05em;
+  }
+
+  .title {
+    font-family: var(--font-structure);
+    font-size: var(--type-3xl);
+    font-weight: 700;
+    color: var(--text-primary);
+    line-height: var(--leading-tight);
+    letter-spacing: -0.02em;
+    margin-top: var(--space-2);
+  }
+
+  .meta {
+    font-family: var(--font-structure);
+    font-size: var(--type-sm);
+    font-weight: 400;
+    color: var(--text-tertiary);
+    line-height: var(--leading-normal);
+    margin-top: var(--space-2);
+  }
+
+  @media (max-width: 719px) {
+    .post-header {
+      padding-top: var(--space-6);
+      padding-bottom: var(--space-6);
+    }
+
+    .title {
+      font-size: var(--type-2xl);
+      line-height: var(--leading-snug);
+    }
+  }
+
+  @media (max-width: 479px) {
+    .post-header {
+      padding-top: var(--space-5);
+      padding-bottom: var(--space-5);
+    }
+
+    .title {
+      font-size: var(--type-xl);
+      line-height: var(--leading-snug);
+    }
+  }
+</style>
\ No newline at end of file
diff --git a/tests/check-post-header.mjs b/tests/check-post-header.mjs
new file mode 100644
index 0000000..5b16b07
--- /dev/null
+++ b/tests/check-post-header.mjs
@@ -0,0 +1,159 @@
+/**
+ * Build-output test for PostHeader.astro
+ * Checks source content for expected structure, props, styles, and responsive breakpoints.
+ */
+import { readFileSync, existsSync } from 'fs';
+import { resolve } from 'path';
+
+const srcPath = resolve('src/components/PostHeader.astro');
+
+let failures = 0;
+let passes = 0;
+
+function assert(condition, label) {
+  if (condition) {
+    console.log(`  ✓ ${label}`);
+    passes++;
+  } else {
+    console.error(`  ✗ FAIL: ${label}`);
+    failures++;
+  }
+}
+
+// ── Source file existence ──
+console.log('\n--- Source file checks ---');
+
+assert(
+  existsSync(srcPath),
+  'src/components/PostHeader.astro exists'
+);
+
+if (existsSync(srcPath)) {
+  const src = readFileSync(srcPath, 'utf-8');
+
+  // ── Props interface ──
+  console.log('\n--- Props interface checks ---');
+
+  assert(
+    /title:\s*string/.test(src),
+    'Props has title: string'
+  );
+  assert(
+    /date:\s*Date/.test(src),
+    'Props has date: Date'
+  );
+  assert(
+    /type\?:\s*string/.test(src),
+    'Props has type?: string'
+  );
+  assert(
+    /readingTime\?:\s*number/.test(src),
+    'Props has readingTime?: number'
+  );
+
+  // ── Default values ──
+  console.log('\n--- Default value checks ---');
+
+  assert(
+    src.includes("'post'") || src.includes('"post"'),
+    'type defaults to "post"'
+  );
+
+  // ── Date formatting ──
+  console.log('\n--- Date formatting checks ---');
+
+  assert(
+    src.includes("toLocaleDateString('en-US'") || src.includes('toLocaleDateString("en-US"'),
+    'Uses toLocaleDateString with en-US locale'
+  );
+  assert(
+    src.includes("'numeric'") || src.includes('"numeric"'),
+    'Date format includes numeric option'
+  );
+  assert(
+    src.includes("'long'") || src.includes('"long"'),
+    'Date format includes long month'
+  );
+  assert(
+    src.includes("toISOString()"),
+    'Computes ISO date string'
+  );
+
+  // ── HTML structure ──
+  console.log('\n--- HTML structure checks ---');
+
+  assert(
+    src.includes('post-header'),
+    'Has .post-header class'
+  );
+  assert(
+    /<header[\s>]/.test(src),
+    'Uses <header> element'
+  );
+  assert(
+    src.includes('badge'),
+    'Has .badge class'
+  );
+  assert(
+    /<span[^>]*class.*badge/.test(src) || /<span[^>]*badge/.test(src),
+    'Badge uses <span> element'
+  );
+  assert(
+    /<h1/.test(src),
+    'Has <h1> element for title'
+  );
+  assert(
+    src.includes('title') && src.includes('class'),
+    'Has .title class'
+  );
+  assert(
+    /<p[^>]*class.*meta/.test(src) || src.includes("class=\"meta\"") || src.includes("class='meta'"),
+    'Meta uses <p> element with .meta class'
+  );
+  assert(
+    /<time[^>]*datetime/.test(src),
+    'Has <time> element with datetime attribute'
+  );
+  assert(
+    src.includes('min read'),
+    'Has reading time display text'
+  );
+  assert(
+    src.includes('readingTime'),
+    'Conditionally shows readingTime'
+  );
+
+  // ── Styles ──
+  console.log('\n--- Style checks ---');
+
+  assert(src.includes('--width-prose'), 'Uses prose max-width');
+  assert(src.includes('--font-structure'), 'Uses structure font');
+  assert(src.includes('--type-xs'), 'Badge uses type-xs');
+  assert(src.includes('--type-3xl'), 'Title uses type-3xl');
+  assert(src.includes('--type-sm'), 'Meta uses type-sm');
+  assert(src.includes('--accent-primary'), 'Badge uses accent-primary');
+  assert(src.includes('--text-primary'), 'Title uses text-primary');
+  assert(src.includes('--text-tertiary'), 'Meta uses text-tertiary');
+  assert(src.includes('--leading-tight'), 'Title uses leading-tight');
+  assert(src.includes('uppercase'), 'Badge is uppercase');
+  assert(src.includes('0.05em'), 'Badge has 0.05em tracking');
+  assert(src.includes('-0.02em'), 'Title has -0.02em tracking');
+
+  // ── Responsive breakpoints ──
+  console.log('\n--- Responsive breakpoint checks ---');
+
+  assert(src.includes('719px'), 'Has 719px breakpoint');
+  assert(src.includes('479px'), 'Has 479px breakpoint');
+  assert(src.includes('--type-2xl'), 'Uses type-2xl at tablet breakpoint');
+  assert(src.includes('--type-xl'), 'Uses type-xl at mobile breakpoint');
+  assert(src.includes('--leading-snug'), 'Uses leading-snug at smaller breakpoints');
+  assert(src.includes('--space-6'), 'Uses space-6 at tablet breakpoint');
+  assert(src.includes('--space-5'), 'Uses space-5 at mobile breakpoint');
+}
+
+// ── Summary ──
+console.log(`\n--- Results: ${passes} passed, ${failures} failed ---`);
+
+if (failures > 0) {
+  process.exit(1);
+}
\ No newline at end of file