diff --git a/tests/metrics-data.test.mjs b/tests/metrics-data.test.mjs
new file mode 100644
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+++ b/tests/metrics-data.test.mjs
@@ -0,0 +1,190 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { readFileSync } from 'node:fs';
+
+const repoRoot = new URL('..', import.meta.url);
+
+const metrics = JSON.parse(
+  readFileSync(new URL('data/metrics.json', repoRoot), 'utf8'),
+);
+
+// These assertions cover the render contract that
+// src/components/MetricsDashboard/index.js depends on but
+// scripts/validate-metrics.mjs does not enforce. The validator is tolerant
+// where the component is not: it reads `data.omitted || []` and only checks
+// `Array.isArray(chart.values)`, while the component dereferences
+// `metricsData.omitted.map(...)` and `chart.values[0].value` without a guard.
+// A metrics.json that passes `npm run validate:metrics` can still crash
+// `npm run build`, so these invariants are asserted against the real file.
+
+test('omitted is present and an array', () => {
+  // MetricsDashboard calls metricsData.omitted.map(...) with no `|| []`
+  // fallback, so an absent key is a TypeError during the site build even
+  // though validate-metrics.mjs accepts it.
+  assert.ok(
+    Array.isArray(metrics.omitted),
+    'omitted must be an array; the dashboard maps over it unguarded',
+  );
+});
+
+test('every omitted entry carries the id and reason the dashboard renders', () => {
+  for (const item of metrics.omitted) {
+    assert.equal(typeof item.id, 'string');
+    assert.ok(item.id.length > 0);
+    assert.equal(typeof item.reason, 'string');
+    assert.ok(item.reason.length > 0);
+  }
+});
+
+test('metrics is a non-empty array of finite numeric values', () => {
+  assert.ok(Array.isArray(metrics.metrics), 'metrics must be an array');
+  assert.ok(metrics.metrics.length > 0, 'metrics must not be empty');
+  for (const metric of metrics.metrics) {
+    // The dashboard renders metric.value.toLocaleString() as a number, and
+    // validate-metrics.mjs only rejects undefined/null/empty-string, so a
+    // string value passes validation and renders unformatted.
+    assert.ok(
+      Number.isFinite(metric.value),
+      `${metric.id} must have a finite numeric value for toLocaleString()`,
+    );
+  }
+});
+
+test('generatedAt parses as a date the dashboard can format', () => {
+  assert.ok(
+    !Number.isNaN(Date.parse(metrics.generatedAt)),
+    'generatedAt must be parseable by new Date() for Intl.DateTimeFormat',
+  );
+});
+
+test('every breakdown has a non-empty values array', () => {
+  const breakdowns = Object.entries(metrics.breakdowns ?? {});
+  assert.ok(breakdowns.length > 0, 'expected at least one breakdown');
+  for (const [id, chart] of breakdowns) {
+    // validate-metrics.mjs accepts `values: []`, but the dashboard reads
+    // chart.values[0].value as the bar-width divisor, which throws on empty.
+    assert.ok(Array.isArray(chart.values), `${id} values must be an array`);
+    assert.ok(
+      chart.values.length > 0,
+      `${id} values must not be empty; the dashboard reads values[0].value`,
+    );
+  }
+});
+
+test('every breakdown uses a positive first value as its bar-width divisor', () => {
+  for (const [id, chart] of Object.entries(metrics.breakdowns ?? {})) {
+    // A zero divisor is finite, so the validator accepts it, but it makes
+    // every bar width NaN.
+    assert.ok(
+      Number.isFinite(chart.values[0].value) && chart.values[0].value > 0,
+      `${id} values[0].value must be > 0 to divide bar widths by`,
+    );
+  }
+});
+
+test('breakdown values are sorted newest-largest first', () => {
+  for (const [id, chart] of Object.entries(metrics.breakdowns ?? {})) {
+    // Bar width is item.value / values[0].value * 100, so anything larger
+    // than values[0] overflows its track.
+    for (const [index, item] of chart.values.entries()) {
+      if (index === 0) continue;
+      assert.ok(
+        chart.values[index - 1].value >= item.value,
+        `${id} values must be sorted descending so no bar exceeds 100% width`,
+      );
+    }
+  }
+});
+
+test('every breakdown entry has the name the dashboard keys rows by', () => {
+  for (const [id, chart] of Object.entries(metrics.breakdowns ?? {})) {
+    const names = chart.values.map((item) => item.name);
+    for (const name of names) {
+      assert.equal(
+        typeof name,
+        'string',
+        `${id} breakdown name must be a string`,
+      );
+      assert.ok(name.length > 0, `${id} breakdown name must not be empty`);
+    }
+    assert.equal(
+      new Set(names).size,
+      names.length,
+      `${id} breakdown names must be unique; they are used as React keys`,
+    );
+  }
+});
+
+test('lifecycle trends expose the shape Sparkline consumes', () => {
+  // validate-metrics.mjs validates referenceArchitectureLifecycle.cards and
+  // .omitted but never inspects .trends, so nothing else checks this shape.
+  const trends = metrics.referenceArchitectureLifecycle?.trends ?? {};
+  assert.ok(
+    Object.keys(trends).length > 0,
+    'expected at least one lifecycle trend',
+  );
+  for (const [id, trend] of Object.entries(trends)) {
+    assert.equal(typeof trend.label, 'string', `${id} trend needs a label`);
+    assert.ok(trend.label.length > 0, `${id} trend label must not be empty`);
+    assert.ok(
+      Array.isArray(trend.values),
+      `${id} trend values must be an array; Sparkline maps over it`,
+    );
+    for (const point of trend.values) {
+      // Sparkline renders values[0].date and values.at(-1).date into its
+      // aria-label and divides by the max value.
+      assert.ok(
+        point.date,
+        `${id} trend point needs a date for the aria-label`,
+      );
+      assert.ok(
+        Number.isFinite(point.value),
+        `${id} trend point value must be a finite number`,
+      );
+    }
+  }
+});
+
+test('lifecycle cards expose the value the dashboard formats', () => {
+  const cards = metrics.referenceArchitectureLifecycle?.cards ?? [];
+  assert.ok(cards.length > 0, 'expected at least one lifecycle card');
+  for (const card of cards) {
+    assert.ok(card.id, 'lifecycle card needs an id for its React key');
+    assert.ok(card.label, `${card.id} needs a label`);
+    assert.ok(
+      Number.isFinite(card.value),
+      `${card.id} value must be finite for toLocaleString()`,
+    );
+  }
+});
+
+test('every series has ordered points the line chart can plot', () => {
+  const series = Object.entries(metrics.series ?? {});
+  assert.ok(series.length > 0, 'expected at least one series');
+  for (const [id, entry] of series) {
+    assert.ok(entry.label, `${id} series needs a label`);
+    assert.ok(entry.sourceUrl, `${id} series needs a sourceUrl`);
+    assert.ok(
+      Array.isArray(entry.values) && entry.values.length > 0,
+      `${id} series must have at least one point`,
+    );
+    // pointY divides by the max value, and the chart range renders
+    // values[0].date alongside values.at(-1).date, so points must run
+    // oldest-first for that range to read correctly.
+    for (const [index, point] of entry.values.entries()) {
+      assert.ok(
+        !Number.isNaN(Date.parse(point.date)),
+        `${id} series point ${index} needs a parseable date`,
+      );
+      assert.ok(
+        Number.isFinite(point.value),
+        `${id} series point ${index} needs a finite value`,
+      );
+      if (index === 0) continue;
+      assert.ok(
+        Date.parse(entry.values[index - 1].date) <= Date.parse(point.date),
+        `${id} series points must run oldest first`,
+      );
+    }
+  }
+});