diff --git a/.github/scripts/csharp-workflow-policy.test.mjs b/.github/scripts/csharp-workflow-policy.test.mjs
index 1a9837f..d7388ba 100755
--- a/.github/scripts/csharp-workflow-policy.test.mjs
+++ b/.github/scripts/csharp-workflow-policy.test.mjs
@@ -135,6 +135,15 @@ test("builds PDF and API documentation in parallel before publishing both", () =
   );
 });
 
+test("validates generated API pages before upload and after download", () => {
+  const documentation = jobs.get("buildDocumentation");
+  const publisher = jobs.get("publishDocumentation");
+
+  assert.match(documentation, /docfx" docfx\.json --warningsAsErrors/);
+  assert.match(documentation, /validate-csharp-docs\.sh _site/);
+  assert.match(publisher, /validate-csharp-docs\.sh _site/);
+});
+
 test("aggregates every job result so skipped dependents cannot hide failures", () => {
   const gate = jobs.get("pipelineStatus");
   assert.ok(gate, "pipelineStatus job should exist");
diff --git a/.github/scripts/validate-csharp-docs.sh b/.github/scripts/validate-csharp-docs.sh
new file mode 100755
index 0000000..1043036
--- /dev/null
+++ b/.github/scripts/validate-csharp-docs.sh
@@ -0,0 +1,18 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+site=${1:?Usage: validate-csharp-docs.sh SITE_DIRECTORY}
+
+for file in \
+  index.html \
+  api/Platform.Interfaces.html \
+  api/Platform.Interfaces.IFactory-1.html \
+  xrefmap.yml; do
+  if [[ ! -s "$site/$file" ]]; then
+    echo "Documentation site is missing $site/$file." >&2
+    exit 1
+  fi
+done
+
+echo "Validated DocFX home page, API pages, and cross-reference map."
diff --git a/.github/scripts/validate-csharp-docs.test.mjs b/.github/scripts/validate-csharp-docs.test.mjs
new file mode 100644
index 0000000..c8b54e5
--- /dev/null
+++ b/.github/scripts/validate-csharp-docs.test.mjs
@@ -0,0 +1,46 @@
+#!/usr/bin/env node
+
+import assert from "node:assert/strict";
+import { mkdtempSync, mkdirSync, rmSync, writeFileSync } from "node:fs";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { spawnSync } from "node:child_process";
+import test from "node:test";
+
+const validator = new URL("./validate-csharp-docs.sh", import.meta.url).pathname;
+
+const withSite = (files, check) => {
+  const site = mkdtempSync(join(tmpdir(), "csharp-docs-"));
+  try {
+    for (const file of files) {
+      const path = join(site, file);
+      mkdirSync(join(path, ".."), { recursive: true });
+      writeFileSync(path, "generated content");
+    }
+    check(spawnSync("bash", [validator, site], { encoding: "utf8" }));
+  } finally {
+    rmSync(site, { recursive: true, force: true });
+  }
+};
+
+const requiredFiles = [
+  "index.html",
+  "api/Platform.Interfaces.html",
+  "api/Platform.Interfaces.IFactory-1.html",
+  "xrefmap.yml",
+];
+
+test("accepts a complete DocFX site", () => {
+  withSite(requiredFiles, ({ status, stderr }) => {
+    assert.equal(status, 0, stderr);
+  });
+});
+
+for (const missingFile of requiredFiles) {
+  test(`rejects a site missing ${missingFile}`, () => {
+    withSite(requiredFiles.filter((file) => file !== missingFile), ({ status, stderr }) => {
+      assert.notEqual(status, 0);
+      assert.ok(stderr.includes(missingFile), stderr);
+    });
+  });
+}
diff --git a/.github/workflows/csharp.yml b/.github/workflows/csharp.yml
index 887c273..7f74576 100644
--- a/.github/workflows/csharp.yml
+++ b/.github/workflows/csharp.yml
@@ -230,7 +230,7 @@ jobs:
           cp _site/README.html _site/index.html
 
       - name: Validate documentation output
-        run: test -s _site/index.html
+        run: ../.github/scripts/validate-csharp-docs.sh _site
 
       - name: Upload documentation site
         timeout-minutes: 5
@@ -263,7 +263,7 @@ jobs:
 
       - name: Validate documentation site
         run: |
-          test -s _site/index.html
+          ../.github/scripts/validate-csharp-docs.sh _site
           test -s _site/Platform.Interfaces.pdf
 
       - name: Publish documentation to gh-pages