diff --git a/apps/scan/src/app/(app)/(home)/resources/register/_components/form.tsx b/apps/scan/src/app/(app)/(home)/resources/register/_components/form.tsx
index 893f5a863..8cff9f08d 100644
--- a/apps/scan/src/app/(app)/(home)/resources/register/_components/form.tsx
+++ b/apps/scan/src/app/(app)/(home)/resources/register/_components/form.tsx
@@ -49,10 +49,15 @@ interface ManualRegistrationResult {
 function getErrorMessageFromRegisterResult(result: {
   success: false;
   error: {
-    type: 'parseErrors' | 'no402';
+    type: 'parseErrors' | 'no402' | 'tunnel';
+    message?: string;
     parseErrors?: string[];
   };
 }): string {
+  if (result.error.type === 'tunnel') {
+    return result.error.message ?? 'Tunnel URLs are not supported';
+  }
+
   if (result.error.type === 'parseErrors') {
     const parseErrors = result.error.parseErrors ?? [];
     if (parseErrors.length > 0) {
diff --git a/apps/scan/src/lib/discovery/register-endpoint.ts b/apps/scan/src/lib/discovery/register-endpoint.ts
index 552b5211f..2999460ec 100644
--- a/apps/scan/src/lib/discovery/register-endpoint.ts
+++ b/apps/scan/src/lib/discovery/register-endpoint.ts
@@ -1,6 +1,7 @@
 import { probeX402Endpoint } from './probe';
 import { registerResource } from '@/lib/resources';
 import { discoverSiblingResources } from './discover-siblings';
+import { isTunnelUrl } from '@/lib/url-helpers';
 
 /**
  * Single orchestrator for registering a single x402 resource.
@@ -16,6 +17,18 @@ export async function registerEndpoint(
     originMetadataFallback?: { title?: string; description?: string };
   }
 ) {
+  // 0. Reject ephemeral tunnel URLs
+  if (isTunnelUrl(url)) {
+    return {
+      success: false as const,
+      error: {
+        type: 'tunnel' as const,
+        message:
+          "Tunnel URLs are ephemeral and can't be reliably discovered by agents. Deploy your API to a permanent URL to register.",
+      },
+    };
+  }
+
   // 1. Probe the endpoint for a 402 response
   const probeResult = await probeX402Endpoint(url);
 
diff --git a/apps/scan/src/lib/url-helpers.test.ts b/apps/scan/src/lib/url-helpers.test.ts
new file mode 100644
index 000000000..461a440d4
--- /dev/null
+++ b/apps/scan/src/lib/url-helpers.test.ts
@@ -0,0 +1,42 @@
+import { describe, it, expect } from 'vitest';
+import { isTunnelUrl } from './url-helpers';
+
+describe('isTunnelUrl', () => {
+  it('detects trycloudflare tunnels', () => {
+    expect(
+      isTunnelUrl(
+        'https://peter-microphone-longitude-lee.trycloudflare.com/api/test'
+      )
+    ).toBe(true);
+  });
+
+  it('detects ngrok tunnels', () => {
+    expect(isTunnelUrl('https://abc123.ngrok.io/path')).toBe(true);
+    expect(isTunnelUrl('https://abc123.ngrok-free.app/path')).toBe(true);
+    expect(isTunnelUrl('https://abc123.ngrok.app/path')).toBe(true);
+  });
+
+  it('detects other tunnel services', () => {
+    expect(isTunnelUrl('https://abc.loca.lt')).toBe(true);
+    expect(isTunnelUrl('https://abc.serveo.net')).toBe(true);
+    expect(isTunnelUrl('https://abc.localhost.run')).toBe(true);
+    expect(isTunnelUrl('https://abc.bore.pub')).toBe(true);
+    expect(isTunnelUrl('https://abc.tunnelmole.com')).toBe(true);
+  });
+
+  it('allows permanent domains', () => {
+    expect(isTunnelUrl('https://api.example.com/path')).toBe(false);
+    expect(isTunnelUrl('https://stableenrich.dev/api')).toBe(false);
+    expect(isTunnelUrl('https://x402scan.com')).toBe(false);
+  });
+
+  it('does not false-positive on domains containing tunnel names', () => {
+    expect(isTunnelUrl('https://ngrok-docs.example.com')).toBe(false);
+    expect(isTunnelUrl('https://my-trycloudflare.com')).toBe(false);
+  });
+
+  it('returns false for invalid URLs', () => {
+    expect(isTunnelUrl('not-a-url')).toBe(false);
+    expect(isTunnelUrl('')).toBe(false);
+  });
+});
diff --git a/apps/scan/src/lib/url-helpers.ts b/apps/scan/src/lib/url-helpers.ts
index 97b22139f..e909908f7 100644
--- a/apps/scan/src/lib/url-helpers.ts
+++ b/apps/scan/src/lib/url-helpers.ts
@@ -39,6 +39,33 @@ export function isLocalUrl(url: string): boolean {
   }
 }
 
+const TUNNEL_DOMAIN_SUFFIXES = [
+  'trycloudflare.com',
+  'ngrok.io',
+  'ngrok-free.app',
+  'ngrok.app',
+  'loca.lt',
+  'serveo.net',
+  'localhost.run',
+  'bore.pub',
+  'tunnelmole.com',
+];
+
+/**
+ * Checks if a URL points to a known ephemeral tunnel service whose
+ * addresses are not stable enough for agent discovery.
+ */
+export function isTunnelUrl(url: string): boolean {
+  try {
+    const hostname = new URL(url).hostname.toLowerCase();
+    return TUNNEL_DOMAIN_SUFFIXES.some(
+      suffix => hostname === suffix || hostname.endsWith(`.${suffix}`)
+    );
+  } catch {
+    return false;
+  }
+}
+
 /**
  * Extracts the port number from a URL, with sensible defaults.
  */
diff --git a/apps/scan/src/services/discovery/fetch-discovery.ts b/apps/scan/src/services/discovery/fetch-discovery.ts
index 0b97f4090..e4948b759 100644
--- a/apps/scan/src/services/discovery/fetch-discovery.ts
+++ b/apps/scan/src/services/discovery/fetch-discovery.ts
@@ -1,7 +1,7 @@
 import { discoverOriginSchema } from '@agentcash/discovery';
 
 import { getOriginFromUrl } from '@/lib/url';
-import { isLocalUrl } from '@/lib/url-helpers';
+import { isLocalUrl, isTunnelUrl } from '@/lib/url-helpers';
 
 import type {
   DiscoveredResource,
@@ -42,6 +42,15 @@ export async function fetchDiscoveryDocument(
     };
   }
 
+  if (isTunnelUrl(origin)) {
+    return {
+      success: false,
+      resources: [],
+      error:
+        "Tunnel URLs are ephemeral and can't be reliably discovered by agents. Deploy your API to a permanent URL to register.",
+    };
+  }
+
   const signal = AbortSignal.timeout(FETCH_TIMEOUT_MS);
   const headers: Record<string, string> = bustCache
     ? { 'Cache-Control': 'no-cache, no-store' }