diff --git a/src/tools/privateHost.test.ts b/src/tools/privateHost.test.ts
new file mode 100644
index 0000000..6209127
--- /dev/null
+++ b/src/tools/privateHost.test.ts
@@ -0,0 +1,70 @@
+// Private/internal-host classification test cases for the SSRF gate.
+//
+// Only the pure literal-classification path is covered here — privateHostReason
+// falls back to a real DNS lookup for names, which a unit test must not do.
+
+import { describe, expect, it } from 'vitest';
+import { parseHTTPURL, privateHostReason } from './privateHost.js';
+
+describe('privateHostReason (IP literals)', () => {
+  const cases: Array<{ host: string; want: boolean; note?: string }> = [
+    // loopback / RFC1918 / link-local
+    { host: '127.0.0.1', want: true },
+    { host: '10.1.2.3', want: true },
+    { host: '172.16.0.1', want: true },
+    { host: '192.168.1.1', want: true },
+    { host: '169.254.169.254', want: true, note: 'cloud metadata' },
+    { host: '0.0.0.0', want: true },
+
+    // RFC 6598 shared address space (100.64.0.0/10)
+    { host: '100.64.0.1', want: true, note: 'lower bound' },
+    { host: '100.100.100.100', want: true, note: 'tailscale MagicDNS resolver' },
+    { host: '100.127.255.255', want: true, note: 'upper bound' },
+
+    // adjacent public space that must NOT be flagged
+    { host: '100.63.255.255', want: false, note: 'just below 100.64/10' },
+    { host: '100.128.0.1', want: false, note: 'just above 100.64/10' },
+    { host: '8.8.8.8', want: false },
+    { host: '172.32.0.1', want: false, note: 'just above RFC1918 172.16/12' },
+    { host: '172.15.0.1', want: false, note: 'just below RFC1918 172.16/12' },
+
+    // IPv6
+    { host: '::1', want: true },
+    { host: 'fe80::1', want: true },
+    { host: 'fd00::1', want: true },
+    { host: '::ffff:127.0.0.1', want: true, note: 'IPv4-mapped loopback' },
+    { host: '2606:4700:4700::1111', want: false },
+  ];
+
+  for (const { host, want, note } of cases) {
+    const label = note ? `${host} (${note})` : host;
+    it(`${want ? 'flags' : 'allows'} ${label}`, async () => {
+      const reason = await privateHostReason(host);
+      expect(Boolean(reason)).toBe(want);
+    });
+  }
+
+  it('normalizes a trailing FQDN dot', async () => {
+    expect(await privateHostReason('localhost.')).toBeTruthy();
+  });
+
+  it('normalizes bracketed IPv6', async () => {
+    expect(await privateHostReason('[::1]')).toBeTruthy();
+  });
+});
+
+describe('parseHTTPURL', () => {
+  it('accepts http and https', () => {
+    expect(parseHTTPURL('http://example.com/').protocol).toBe('http:');
+    expect(parseHTTPURL('https://example.com/').protocol).toBe('https:');
+  });
+
+  it('rejects non-http(s) schemes', () => {
+    expect(() => parseHTTPURL('file:///etc/passwd')).toThrow(/unsupported URL scheme/);
+    expect(() => parseHTTPURL('gopher://example.com/')).toThrow(/unsupported URL scheme/);
+  });
+
+  it('rejects a malformed URL', () => {
+    expect(() => parseHTTPURL('not a url')).toThrow(/invalid URL/);
+  });
+});
diff --git a/src/tools/privateHost.ts b/src/tools/privateHost.ts
index a67be88..c4e696d 100644
--- a/src/tools/privateHost.ts
+++ b/src/tools/privateHost.ts
@@ -104,6 +104,12 @@ function privateIPv4Reason(host: string): string {
   if (a === 169 && b === 254) return 'link-local/metadata IPv4';
   if (a === 172 && b >= 16 && b <= 31) return 'RFC1918 private IPv4';
   if (a === 192 && b === 168) return 'RFC1918 private IPv4';
+  // RFC 6598 shared address space (100.64.0.0/10). Not publicly routable, and in
+  // practice this is where real internal infrastructure lives: Tailscale/WireGuard
+  // overlays (incl. the 100.100.100.100 MagicDNS resolver), carrier-grade NAT, and
+  // several cloud providers' internal service endpoints. Without this a web_fetch
+  // at a tailnet host is reached silently, with no gate prompt.
+  if (a === 100 && b !== undefined && b >= 64 && b <= 127) return 'RFC6598 shared address space IPv4';
   if (a === 0) return 'this-network IPv4';
   return '';
 }