diff --git a/content/product-story.json b/content/product-story.json
new file mode 100644
index 0000000..a696c6f
--- /dev/null
+++ b/content/product-story.json
@@ -0,0 +1,58 @@
+{
+  "schemaVersion": "1.0",
+  "audience": "Developers who document and review their technology stack in source control, often with a coding agent.",
+  "job": "Turn a readable description of services, data stores, boundaries, and connections into a diagram for a README or architecture review, and keep it current as the system changes.",
+  "alternatives": "Manual drawing requires maintaining coordinates and styling. General-purpose diagram languages prioritize broader diagram types. Stack focuses on semantic technology-stack documents, theme-managed presentation, and a shared local renderer.",
+  "hero": {
+    "name": "Stack",
+    "tagline": "Write your stack. Get a beautiful diagram.",
+    "description": "Describe your services and connections in text. Stack handles layout and theming, then renders a shareable SVG in your terminal or browser.",
+    "primaryAction": { "text": "Create your first diagram", "link": "/guide/getting-started" },
+    "secondaryAction": { "text": "Try the Playground", "link": "https://stack-diagram.com/" }
+  },
+  "features": [
+    {
+      "id": "beautiful-by-default",
+      "title": "Beautiful by default",
+      "details": "Describe the system, not every box. Automatic layout and coordinated themes keep your diagrams polished without manual positioning or styling.",
+      "evidence": [
+        "https://github.com/stack-sh/theme/blob/main/CONTRACT.md",
+        "https://github.com/stack-sh/engine/tree/main/layout-corpus"
+      ]
+    },
+    {
+      "id": "consistent-everywhere",
+      "title": "Consistent everywhere",
+      "details": "Move between your coding agent, terminal, and browser. The shared engine keeps the same source, theme, and icon packs consistent across workflows.",
+      "evidence": [
+        "https://github.com/stack-sh/engine/blob/main/README.md",
+        "https://github.com/stack-sh/web/blob/main/src/lib/stack-engine.ts",
+        "https://github.com/stack-sh/cli/blob/main/Cargo.toml"
+      ]
+    },
+    {
+      "id": "fast-local-rendering",
+      "title": "Fast, local rendering",
+      "details": "Edit, render, and repeat without a rendering server. Keep your source on your device and export standalone SVG without scripts or external assets.",
+      "evidence": [
+        "https://github.com/stack-sh/engine/blob/main/layout-corpus/README.md#runtime-budget",
+        "https://github.com/stack-sh/engine/blob/main/README.md"
+      ]
+    }
+  ],
+  "firstSuccess": [
+    "Choose the CLI for terminal or coding-agent workflows, or open the Playground without installation.",
+    "Install the CLI through one supported channel; add the optional skill with npx skills add stack-sh/cli.",
+    "Run stack init, check, and render in an empty directory; browser users edit the example and select Run.",
+    "Open or download the SVG, change the source, and render again.",
+    "Explore themes and examples, then provider icons, configuration, and the language reference."
+  ],
+  "claimBoundaries": [
+    "No unmeasured claim that Stack is faster or more beautiful than Mermaid or any other product.",
+    "Cross-workflow consistency assumes matching engine versions, source, theme, and caller-supplied icon packs; it is not a promise across arbitrary versions or fonts in a downstream SVG viewer.",
+    "Fast describes a short local iteration loop, supported by the reproducible corpus benchmark. Native warm-render measurements are not browser cold-start measurements or universal latency guarantees.",
+    "Local rendering does not mean installing tools and loading the website require no network. The engine does not send diagram source to a rendering service.",
+    "Safe SVG means constrained engine output, not immunity from every defect. Third-party icon packs require explicit import and retain their own terms.",
+    "User-facing examples render canonical .stack source with the current site's WASM engine at runtime. Do not publish pre-rendered example SVG as a second source of truth. Approved regression snapshots remain a separate test artifact."
+  ]
+}
diff --git a/scripts/product-story.test.mjs b/scripts/product-story.test.mjs
new file mode 100644
index 0000000..a1a1552
--- /dev/null
+++ b/scripts/product-story.test.mjs
@@ -0,0 +1,23 @@
+import assert from 'node:assert/strict';
+import { readFile } from 'node:fs/promises';
+import test from 'node:test';
+
+test('canonical story has one product heading, three evidenced benefits, and both first-success paths', async () => {
+  const story = JSON.parse(await readFile(new URL('../content/product-story.json', import.meta.url), 'utf8'));
+  assert.equal(story.schemaVersion, '1.0');
+  assert.equal(story.hero.name, 'Stack');
+  assert.equal(story.features.length, 3);
+  assert.equal(new Set(story.features.map(feature => feature.id)).size, 3);
+  for (const feature of story.features) {
+    assert.ok(feature.title.length > 0 && feature.title.length <= 40);
+    assert.ok(feature.details.length > 0 && feature.details.length <= 220);
+    assert.ok(feature.evidence.length > 0);
+    for (const evidence of feature.evidence) assert.ok(evidence.startsWith('https://github.com/stack-sh/'));
+  }
+  assert.equal(story.hero.primaryAction.link, '/guide/getting-started');
+  assert.equal(story.hero.secondaryAction.link, 'https://stack-diagram.com/');
+  assert.match(story.firstSuccess.join('\n'), /npx skills add stack-sh\/cli/);
+  assert.match(story.firstSuccess.join('\n'), /Playground/);
+  assert.match(story.claimBoundaries.join('\n'), /matching engine versions/);
+  assert.match(story.claimBoundaries.join('\n'), /runtime/);
+});