diff --git a/apps/web/src/app/api/marketing-tags/gtm/route.ts b/apps/web/src/app/api/marketing-tags/gtm/route.ts
new file mode 100644
index 000000000..906d5697b
--- /dev/null
+++ b/apps/web/src/app/api/marketing-tags/gtm/route.ts
@@ -0,0 +1,15 @@
+import { NextResponse } from 'next/server';
+import { buildGoogleTagManagerScript } from '@/lib/marketing-tag-scripts';
+
+export function GET() {
+  if (!process.env.NEXT_PUBLIC_GTM_ID) {
+    return new NextResponse(null, { status: 404 });
+  }
+
+  return new NextResponse(buildGoogleTagManagerScript(process.env.NEXT_PUBLIC_GTM_ID), {
+    headers: {
+      'Content-Type': 'application/javascript; charset=utf-8',
+      'Cache-Control': 'public, max-age=300, s-maxage=300',
+    },
+  });
+}
diff --git a/apps/web/src/app/api/marketing-tags/impact/route.ts b/apps/web/src/app/api/marketing-tags/impact/route.ts
new file mode 100644
index 000000000..42588a198
--- /dev/null
+++ b/apps/web/src/app/api/marketing-tags/impact/route.ts
@@ -0,0 +1,15 @@
+import { NextResponse } from 'next/server';
+import { buildImpactUttScript } from '@/lib/marketing-tag-scripts';
+
+export function GET() {
+  if (!process.env.NEXT_PUBLIC_IMPACT_UTT_ID) {
+    return new NextResponse(null, { status: 404 });
+  }
+
+  return new NextResponse(buildImpactUttScript(process.env.NEXT_PUBLIC_IMPACT_UTT_ID), {
+    headers: {
+      'Content-Type': 'application/javascript; charset=utf-8',
+      'Cache-Control': 'public, max-age=300, s-maxage=300',
+    },
+  });
+}
diff --git a/apps/web/src/app/layout.tsx b/apps/web/src/app/layout.tsx
index 6ec855881..b68d1e9ab 100644
--- a/apps/web/src/app/layout.tsx
+++ b/apps/web/src/app/layout.tsx
@@ -5,7 +5,6 @@ import './globals.css';
 import { PostHogProvider } from '../components/PostHogProvider';
 import { Providers } from '../components/Providers';
 import { DataLayerProvider } from '../components/DataLayerProvider';
-import { GoogleTagManager } from '@next/third-parties/google';
 import { APP_URL } from '@/lib/constants';
 
 const inter = Inter({
@@ -113,13 +112,15 @@ export default function RootLayout({
         </Providers>
 
         {process.env.NEXT_PUBLIC_GTM_ID && (
-          <GoogleTagManager gtmId={process.env.NEXT_PUBLIC_GTM_ID} />
+          <Script
+            id="google-tag-manager"
+            src="/api/marketing-tags/gtm"
+            strategy="afterInteractive"
+          />
         )}
 
         {process.env.NEXT_PUBLIC_IMPACT_UTT_ID && (
-          <Script id="impact-utt" strategy="beforeInteractive">
-            {`(function(a,b,c,d,e,f,g){e.ire_o=c;e[c]=e[c]||function(){(e[c].a=e[c].a||[]).push(arguments)};f=d.createElement(b);g=d.getElementsByTagName(b)[0];f.async=1;f.src=a;g.parentNode.insertBefore(f,g);})('https://utt.impactcdn.com/${process.env.NEXT_PUBLIC_IMPACT_UTT_ID}.js','script','ire',document,window);`}
-          </Script>
+          <Script id="impact-utt" src="/api/marketing-tags/impact" strategy="beforeInteractive" />
         )}
       </body>
     </html>
diff --git a/apps/web/src/components/DataLayerProvider.tsx b/apps/web/src/components/DataLayerProvider.tsx
index 540516234..be81820d0 100644
--- a/apps/web/src/components/DataLayerProvider.tsx
+++ b/apps/web/src/components/DataLayerProvider.tsx
@@ -1,5 +1,6 @@
 'use client';
 
+import type {} from '@/types/datalayer';
 import { useSession } from 'next-auth/react';
 import { useEffect } from 'react';
 
diff --git a/apps/web/src/lib/marketing-tag-scripts.test.ts b/apps/web/src/lib/marketing-tag-scripts.test.ts
new file mode 100644
index 000000000..a5c6167a7
--- /dev/null
+++ b/apps/web/src/lib/marketing-tag-scripts.test.ts
@@ -0,0 +1,20 @@
+import { buildGoogleTagManagerScript, buildImpactUttScript } from '@/lib/marketing-tag-scripts';
+
+describe('marketing tag scripts', () => {
+  it('escapes GTM IDs embedded into bootstrap JavaScript', () => {
+    const script = buildGoogleTagManagerScript('GTM-TEST</script><script>alert(1)</script>');
+
+    expect(script).toContain('GTM-TEST\\u003C\\u002Fscript\\u003E');
+    expect(script).not.toContain('</script>');
+    expect(script).not.toContain('<script>');
+  });
+
+  it('escapes Impact IDs embedded into bootstrap JavaScript', () => {
+    const script = buildImpactUttScript('impact</script><script>alert(1)</script>');
+
+    expect(script).toContain('https:\\u002F\\u002Futt.impactcdn.com\\u002Fimpact');
+    expect(script).toContain('\\u003C\\u002Fscript\\u003E');
+    expect(script).not.toContain('</script>');
+    expect(script).not.toContain('<script>');
+  });
+});
diff --git a/apps/web/src/lib/marketing-tag-scripts.ts b/apps/web/src/lib/marketing-tag-scripts.ts
new file mode 100644
index 000000000..c44b8d31c
--- /dev/null
+++ b/apps/web/src/lib/marketing-tag-scripts.ts
@@ -0,0 +1,28 @@
+function toJavaScriptStringLiteral(value: string): string {
+  return JSON.stringify(value).replace(/[<>/\u2028\u2029]/g, char => {
+    switch (char) {
+      case '<':
+        return '\\u003C';
+      case '>':
+        return '\\u003E';
+      case '/':
+        return '\\u002F';
+      case '\u2028':
+        return '\\u2028';
+      case '\u2029':
+        return '\\u2029';
+      default:
+        return char;
+    }
+  });
+}
+
+export function buildGoogleTagManagerScript(gtmId: string): string {
+  const encodedGtmId = toJavaScriptStringLiteral(gtmId);
+  return `(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer',${encodedGtmId});`;
+}
+
+export function buildImpactUttScript(impactUttId: string): string {
+  const encodedScriptUrl = toJavaScriptStringLiteral(`https://utt.impactcdn.com/${impactUttId}.js`);
+  return `(function(a,b,c,d,e,f,g){e.ire_o=c;e[c]=e[c]||function(){(e[c].a=e[c].a||[]).push(arguments)};f=d.createElement(b);g=d.getElementsByTagName(b)[0];f.async=1;f.src=a;g.parentNode.insertBefore(f,g);})(${encodedScriptUrl},'script','ire',document,window);`;
+}
diff --git a/apps/web/src/lib/security-headers.test.ts b/apps/web/src/lib/security-headers.test.ts
new file mode 100644
index 000000000..2a0f0e2e6
--- /dev/null
+++ b/apps/web/src/lib/security-headers.test.ts
@@ -0,0 +1,82 @@
+import { buildContentSecurityPolicy, getConfiguredConnectSrcOrigins } from '@/lib/security-headers';
+
+describe('security headers', () => {
+  it('builds CSP with required third-party sources', () => {
+    const policy = buildContentSecurityPolicy({
+      connectSrcUrls: ['wss://cloud-agent.example.com/socket'],
+    });
+
+    expect(policy).toContain("default-src 'self'");
+    expect(policy).toContain("script-src 'self' 'unsafe-inline'");
+    expect(policy).toContain('https://js.stripe.com');
+    expect(policy).toContain('https://*.js.stripe.com');
+    expect(policy).toContain('https://api.stripe.com');
+    expect(policy).toContain('https://hooks.stripe.com');
+    expect(policy).toContain('https://login.kilo.ai');
+    expect(policy).toContain('https://login-test.kilo.ai');
+    expect(policy).toContain('https://www.googletagmanager.com');
+    expect(policy).toContain('https://utt.impactcdn.com');
+    expect(policy).toContain('https://challenges.cloudflare.com');
+    expect(policy).toContain('https://cdn.jsdelivr.net');
+    expect(policy).toContain('https://unpkg.com');
+    expect(policy).toContain('https://*.d.kiloapps.io');
+    expect(policy).toContain('https://www.youtube.com');
+    expect(policy).toContain("'wasm-unsafe-eval'");
+    expect(policy).toContain('wss://cloud-agent.example.com');
+  });
+
+  it('adds development-only sources only in development mode', () => {
+    const productionPolicy = buildContentSecurityPolicy({ isDevelopment: false });
+    const developmentPolicy = buildContentSecurityPolicy({ isDevelopment: true });
+
+    expect(productionPolicy).not.toContain("'unsafe-eval'");
+    expect(productionPolicy).not.toContain('ws://localhost:*');
+    expect(developmentPolicy).toContain("'unsafe-eval'");
+    expect(developmentPolicy).toContain('ws://localhost:*');
+  });
+
+  it('derives configured connect-src origins from public URLs', () => {
+    const env: Record<string, string | undefined> = {
+      NEXT_PUBLIC_CLOUD_AGENT_WS_URL: 'wss://agent.example.com/path',
+      NEXT_PUBLIC_CLOUD_AGENT_NEXT_WS_URL: 'wss://next-agent.example.com/path',
+      NEXT_PUBLIC_SESSION_INGEST_WS_URL: 'wss://ingest.example.com/path',
+      NEXT_PUBLIC_GASTOWN_URL: 'https://gastown.example.com/api',
+    };
+
+    expect(getConfiguredConnectSrcOrigins(env)).toEqual([
+      'wss://agent.example.com',
+      'wss://next-agent.example.com',
+      'wss://ingest.example.com',
+      'https://gastown.example.com',
+    ]);
+  });
+
+  it('allows extra CSP sources through directive-specific env vars', () => {
+    const policy = buildContentSecurityPolicy({
+      env: {
+        CSP_ADDITIONAL_SCRIPT_SRC: 'https://tag.example.com, https://cdn.example.com',
+        CSP_ADDITIONAL_CONNECT_SRC: 'https://api.example.com',
+        CSP_ADDITIONAL_IMG_SRC: 'https://images.example.com',
+        CSP_ADDITIONAL_FRAME_SRC: 'https://frames.example.com',
+      },
+    });
+
+    expect(policy).toContain('script-src');
+    expect(policy).toContain('https://tag.example.com');
+    expect(policy).toContain('https://cdn.example.com');
+    expect(policy).toContain('https://api.example.com');
+    expect(policy).toContain('https://images.example.com');
+    expect(policy).toContain('https://frames.example.com');
+  });
+
+  it('ignores additional CSP sources that would inject directives', () => {
+    const policy = buildContentSecurityPolicy({
+      env: {
+        CSP_ADDITIONAL_SCRIPT_SRC: 'https://good.example.com; object-src *',
+      },
+    });
+
+    expect(policy).not.toContain('https://good.example.com;');
+    expect(policy).not.toContain('object-src *');
+  });
+});
diff --git a/apps/web/src/lib/security-headers.ts b/apps/web/src/lib/security-headers.ts
new file mode 100644
index 000000000..6c3e36a16
--- /dev/null
+++ b/apps/web/src/lib/security-headers.ts
@@ -0,0 +1,153 @@
+type CspDirective =
+  | 'script-src'
+  | 'connect-src'
+  | 'img-src'
+  | 'style-src'
+  | 'font-src'
+  | 'frame-src'
+  | 'worker-src'
+  | 'media-src';
+
+export type ContentSecurityPolicyOptions = {
+  isDevelopment?: boolean;
+  connectSrcUrls?: Array<string | undefined>;
+  env?: Record<string, string | undefined>;
+};
+
+const ADDITIONAL_SOURCE_ENV_BY_DIRECTIVE = {
+  'script-src': 'CSP_ADDITIONAL_SCRIPT_SRC',
+  'connect-src': 'CSP_ADDITIONAL_CONNECT_SRC',
+  'img-src': 'CSP_ADDITIONAL_IMG_SRC',
+  'style-src': 'CSP_ADDITIONAL_STYLE_SRC',
+  'font-src': 'CSP_ADDITIONAL_FONT_SRC',
+  'frame-src': 'CSP_ADDITIONAL_FRAME_SRC',
+  'worker-src': 'CSP_ADDITIONAL_WORKER_SRC',
+  'media-src': 'CSP_ADDITIONAL_MEDIA_SRC',
+} satisfies Record<CspDirective, string>;
+
+function compactUnique(values: Array<string | null | undefined>): string[] {
+  const compacted = values.filter((value): value is string => Boolean(value && value.length > 0));
+  return Array.from(new Set(compacted));
+}
+
+function originFromUrl(value: string | undefined): string | null {
+  if (!value) return null;
+  try {
+    return new URL(value).origin;
+  } catch {
+    return null;
+  }
+}
+
+function parseAdditionalCspSources(value: string | undefined): string[] {
+  if (!value || value.includes(';')) return [];
+  return compactUnique(
+    value
+      .split(/[\s,]+/)
+      .map(source => source.trim())
+      .filter(source => source.length > 0)
+  );
+}
+
+function getAdditionalCspSources(
+  directive: CspDirective,
+  env: Record<string, string | undefined>
+): string[] {
+  return parseAdditionalCspSources(env[ADDITIONAL_SOURCE_ENV_BY_DIRECTIVE[directive]]);
+}
+
+export function getConfiguredConnectSrcOrigins(
+  env: Record<string, string | undefined> = process.env
+): string[] {
+  return compactUnique([
+    originFromUrl(env.NEXT_PUBLIC_CLOUD_AGENT_WS_URL),
+    originFromUrl(env.NEXT_PUBLIC_CLOUD_AGENT_NEXT_WS_URL),
+    originFromUrl(env.NEXT_PUBLIC_SESSION_INGEST_WS_URL),
+    originFromUrl(env.NEXT_PUBLIC_GASTOWN_URL),
+  ]);
+}
+
+export function buildContentSecurityPolicy({
+  isDevelopment = false,
+  connectSrcUrls,
+  env = process.env,
+}: ContentSecurityPolicyOptions = {}): string {
+  const configuredConnectSrcUrls = connectSrcUrls ?? getConfiguredConnectSrcOrigins(env);
+  const scriptSrc = compactUnique([
+    "'self'",
+    "'unsafe-inline'",
+    "'wasm-unsafe-eval'",
+    isDevelopment ? "'unsafe-eval'" : null,
+    'https://www.googletagmanager.com',
+    'https://utt.impactcdn.com',
+    'https://login.kilo.ai',
+    'https://login-test.kilo.ai',
+    'https://js.stripe.com',
+    'https://*.js.stripe.com',
+    'https://checkout.stripe.com',
+    'https://challenges.cloudflare.com',
+    ...getAdditionalCspSources('script-src', env),
+  ]);
+
+  const connectSrc = compactUnique([
+    "'self'",
+    'https://auth.kilo.ai',
+    'https://us.i.posthog.com',
+    'https://us-assets.i.posthog.com',
+    'https://api.stripe.com',
+    'https://r.stripe.com',
+    'https://m.stripe.com',
+    'https://checkout.stripe.com',
+    'https://utt.impactcdn.com',
+    'https://challenges.cloudflare.com',
+    'https://cdn.jsdelivr.net',
+    'https://unpkg.com',
+    'https://*.d.kiloapps.io',
+    isDevelopment ? 'http://localhost:*' : null,
+    isDevelopment ? 'ws://localhost:*' : null,
+    ...configuredConnectSrcUrls.map(originFromUrl),
+    ...getAdditionalCspSources('connect-src', env),
+  ]);
+
+  const directives: Record<string, string[]> = {
+    'default-src': ["'self'"],
+    'base-uri': ["'self'"],
+    'object-src': ["'none'"],
+    'frame-ancestors': ["'self'"],
+    'form-action': ["'self'"],
+    'script-src': scriptSrc,
+    'connect-src': connectSrc,
+    'img-src': [
+      "'self'",
+      'data:',
+      'blob:',
+      'https://lh3.googleusercontent.com',
+      'https://avatars.githubusercontent.com',
+      'https://*.stripe.com',
+      'https://www.googletagmanager.com',
+      'https://utt.impactcdn.com',
+      'https://challenges.cloudflare.com',
+      ...getAdditionalCspSources('img-src', env),
+    ],
+    'style-src': ["'self'", "'unsafe-inline'", ...getAdditionalCspSources('style-src', env)],
+    'font-src': ["'self'", 'data:', ...getAdditionalCspSources('font-src', env)],
+    'frame-src': [
+      "'self'",
+      'https://js.stripe.com',
+      'https://*.js.stripe.com',
+      'https://hooks.stripe.com',
+      'https://checkout.stripe.com',
+      'https://challenges.cloudflare.com',
+      'https://www.youtube.com',
+      'https://*.d.kiloapps.io',
+      ...getAdditionalCspSources('frame-src', env),
+    ],
+    'worker-src': ["'self'", 'blob:', ...getAdditionalCspSources('worker-src', env)],
+    'media-src': ["'self'", 'blob:', ...getAdditionalCspSources('media-src', env)],
+    'manifest-src': ["'self'"],
+  };
+
+  return Object.entries(directives)
+    .map(([directive, sources]) => `${directive} ${sources.join(' ')}`)
+    .join('; ');
+}
diff --git a/apps/web/src/proxy.ts b/apps/web/src/proxy.ts
index 58b0b47af..c84783273 100644
--- a/apps/web/src/proxy.ts
+++ b/apps/web/src/proxy.ts
@@ -3,15 +3,27 @@ import { NextResponse } from 'next/server';
 import { withAuthenticatedAdminApiRoutes } from './middleware/withAuthenticatedAdminApiRoutes';
 import { withBlockedClients } from './middleware/withBlockedClients';
 import { withKiloEditorCookie } from './middleware/withKiloEditorCookie';
+import { buildContentSecurityPolicy, getConfiguredConnectSrcOrigins } from '@/lib/security-headers';
 
 function baseProxy(request: NextRequestWithAuth) {
   const requestHeaders = new Headers(request.headers);
   requestHeaders.set('x-pathname', request.nextUrl.pathname);
-  return NextResponse.next({
+
+  const response = NextResponse.next({
     request: {
       headers: requestHeaders,
     },
   });
+
+  response.headers.set(
+    'Content-Security-Policy',
+    buildContentSecurityPolicy({
+      isDevelopment: process.env.NODE_ENV === 'development',
+      connectSrcUrls: getConfiguredConnectSrcOrigins(),
+    })
+  );
+
+  return response;
 }
 
 export const proxy = withBlockedClients(
diff --git a/apps/web/src/types/datalayer.d.ts b/apps/web/src/types/datalayer.d.ts
index d9dbef77f..8e76d60dc 100644
--- a/apps/web/src/types/datalayer.d.ts
+++ b/apps/web/src/types/datalayer.d.ts
@@ -1,6 +1,7 @@
-// Extend the Window interface to include dataLayer
+export {};
+
 declare global {
   interface Window {
-    datalayer: object[];
+    dataLayer?: Array<Record<string, unknown>>;
   }
 }