diff --git a/craft/src/components/forms/CaptchaMock.tsx b/craft/src/components/forms/CaptchaMock.tsx
new file mode 100644
index 0000000..d8dfd49
--- /dev/null
+++ b/craft/src/components/forms/CaptchaMock.tsx
@@ -0,0 +1,21 @@
+import type { CSSProperties } from 'react';
+
+/**
+ * INERT editor-only stand-in for the ALTCHA widget. It makes no network request and loads
+ * no script: the real widget is injected at PUBLISH time by the WHP panel
+ * (FormRelayRewrite.php) once the relay token is known. Never emitted by toHtml.
+ */
+export const CaptchaMock = ({ style }: { style?: CSSProperties }) => (
+  <div
+    data-testid="captcha-mock"
+    aria-hidden="true"
+    style={{
+      display: 'flex', alignItems: 'center', gap: 8, padding: '10px 12px', maxWidth: 260,
+      border: '1px solid rgba(128,128,128,0.4)', borderRadius: 6, fontSize: 13,
+      fontFamily: 'Inter, sans-serif', opacity: 0.85, pointerEvents: 'none', ...style,
+    }}
+  >
+    <span style={{ width: 16, height: 16, border: '2px solid currentColor', borderRadius: 3, display: 'inline-block' }} />
+    I&apos;m not a robot <span style={{ marginLeft: 'auto', fontSize: 10, opacity: 0.6 }}>ALTCHA</span>
+  </div>
+);
diff --git a/craft/src/components/forms/ContactForm.tsx b/craft/src/components/forms/ContactForm.tsx
index f70bd59..42a8958 100644
--- a/craft/src/components/forms/ContactForm.tsx
+++ b/craft/src/components/forms/ContactForm.tsx
@@ -1,6 +1,7 @@
 import React, { CSSProperties } from 'react';
 import { useNode, UserComponent } from '@craftjs/core';
 import { cssPropsToString } from '../../utils/style-helpers';
+import { CaptchaMock } from './CaptchaMock';
 import { relayFormWiring } from '../../utils/form-relay-wiring';
 import { escapeHtml, escapeAttr, slugId, cssValue, sanitizeInputType } from '../../utils/escape';
 import { tokenRef } from '../../utils/tokens';
@@ -54,6 +55,8 @@ interface ContactFormProps {
   webhookUrl?: string;
   webhookSecretId?: string;
   webhookAuthMode?: 'signature' | 'bearer';
+  /** ALTCHA captcha (relay path). undefined = legacy design: no marker attr, stored flag untouched. */
+  captcha?: boolean;
   animation?: string;
   animationDelay?: string;
   hideOnDesktop?: boolean;
@@ -73,6 +76,7 @@ export const ContactForm: UserComponent<ContactFormProps> = ({
   submitText = 'Send Message',
   submitColor = tokenRef('primary'),
   formAction = '#',
+  captcha,
   successMessage = 'Thank you! We\'ll get back to you soon.',
   style = {},
   labelColor = tokenRef('text'),
@@ -150,6 +154,7 @@ export const ContactForm: UserComponent<ContactFormProps> = ({
           )}
         </div>
       ))}
+      {captcha === true && <CaptchaMock />}
       <button
         type="submit"
         style={{
@@ -197,6 +202,7 @@ ContactForm.craft = {
     webhookUrl: '',
     webhookSecretId: '',
     webhookAuthMode: 'signature',
+    captcha: true,
     animation: '',
     animationDelay: '',
     hideOnDesktop: false,
@@ -269,6 +275,7 @@ ContactForm.craft = {
       secretId: props.webhookSecretId,
       authMode: props.webhookAuthMode,
     },
+    props.captcha,
   );
 
   // The form-sender relay delivers success via a full-page 303 redirect
diff --git a/craft/src/components/forms/FormContainer.tsx b/craft/src/components/forms/FormContainer.tsx
index b64a8ce..a7b471a 100644
--- a/craft/src/components/forms/FormContainer.tsx
+++ b/craft/src/components/forms/FormContainer.tsx
@@ -3,6 +3,7 @@ import { tokenRef } from '../../utils/tokens';
 import { useNode, Element, UserComponent } from '@craftjs/core';
 import { Container } from '../layout/Container';
 import { cssPropsToString } from '../../utils/style-helpers';
+import { CaptchaMock } from './CaptchaMock';
 import { relayFormWiring } from '../../utils/form-relay-wiring';
 import { sanitizeFormMethod } from '../../utils/escape';
 
@@ -10,6 +11,8 @@ interface FormContainerProps {
   action?: string;
   method?: 'GET' | 'POST';
   recipientEmail?: string;
+  /** ALTCHA captcha (relay path). undefined = legacy design: no marker attr, stored flag untouched. */
+  captcha?: boolean;
   thankYouUrl?: string;
   style?: CSSProperties;
   children?: React.ReactNode;
@@ -24,6 +27,7 @@ export const FormContainer: UserComponent<FormContainerProps> = ({
   action = '#',
   method = 'POST',
   style = {},
+  captcha,
 }) => {
   const { connectors: { connect, drag } } = useNode();
 
@@ -46,6 +50,7 @@ export const FormContainer: UserComponent<FormContainerProps> = ({
         style={{ display: 'flex', flexDirection: 'column', gap: '16px', padding: '0' }}
         tag="div"
       />
+      {captcha === true && <CaptchaMock style={{ marginTop: 12 }} />}
     </form>
   );
 };
@@ -59,6 +64,7 @@ FormContainer.craft = {
     method: 'POST',
     recipientEmail: '',
     thankYouUrl: '',
+    captcha: true,
     style: {
       padding: '24px',
       backgroundColor: tokenRef('bg'),
@@ -85,7 +91,7 @@ FormContainer.craft = {
     padding: '24px',
     ...props.style,
   });
-  const { useRelay, marker, actionAttr, honeypot } = relayFormWiring(props.recipientEmail, props.thankYouUrl, props.action, nodeId);
+  const { useRelay, marker, actionAttr, honeypot } = relayFormWiring(props.recipientEmail, props.thankYouUrl, props.action, nodeId, undefined, props.captcha);
   const method = useRelay ? 'POST' : sanitizeFormMethod(props.method); // relay requires POST
   const body = honeypot + childrenHtml;                        // honeypot as first child
   return {
diff --git a/craft/src/components/forms/SubscribeForm.tsx b/craft/src/components/forms/SubscribeForm.tsx
index f9c5fc6..ebb9db4 100644
--- a/craft/src/components/forms/SubscribeForm.tsx
+++ b/craft/src/components/forms/SubscribeForm.tsx
@@ -1,6 +1,7 @@
 import React, { CSSProperties } from 'react';
 import { useNode, UserComponent } from '@craftjs/core';
 import { cssPropsToString } from '../../utils/style-helpers';
+import { CaptchaMock } from './CaptchaMock';
 import { relayFormWiring } from '../../utils/form-relay-wiring';
 import { escapeHtml, escapeAttr } from '../../utils/escape';
 import { tokenRef } from '../../utils/tokens';
@@ -25,6 +26,8 @@ interface SubscribeFormProps {
    *  published form then has no working action at all, which is the bug
    *  this prop exists to fix. */
   recipientEmail?: string;
+  /** ALTCHA captcha (relay path). undefined = legacy design: no marker attr, stored flag untouched. */
+  captcha?: boolean;
   thankYouUrl?: string;
   animation?: string;
   animationDelay?: string;
@@ -40,6 +43,7 @@ export const SubscribeForm: UserComponent<SubscribeFormProps> = ({
   buttonColor = tokenRef('primary'),
   layout = 'inline',
   style = {},
+  captcha,
 }) => {
   const {
     connectors: { connect, drag },
@@ -116,6 +120,7 @@ export const SubscribeForm: UserComponent<SubscribeFormProps> = ({
           {buttonText}
         </button>
       </form>
+      {captcha === true && <CaptchaMock style={{ margin: '12px auto 0' }} />}
     </div>
   );
 };
@@ -133,6 +138,7 @@ SubscribeForm.craft = {
     style: { backgroundColor: tokenRef('bg') },
     recipientEmail: '',
     thankYouUrl: '',
+    captcha: true,
     animation: '',
     animationDelay: '',
     hideOnDesktop: false,
@@ -202,7 +208,7 @@ SubscribeForm.craft = {
   // `formAction`-less relay wiring (fallbackAction undefined -> '#') keeps
   // the old no-recipient case visually identical (action="#") while making
   // the relay path actually functional once an admin sets an email.
-  const { marker, actionAttr, honeypot } = relayFormWiring(props.recipientEmail, props.thankYouUrl, undefined, nodeId);
+  const { marker, actionAttr, honeypot } = relayFormWiring(props.recipientEmail, props.thankYouUrl, undefined, nodeId, undefined, props.captcha);
 
   return {
     html: `${marker}<div${wrapperStyle ? ` style="${wrapperStyle}"` : ''}>
diff --git a/craft/src/components/forms/captcha.toHtml.test.ts b/craft/src/components/forms/captcha.toHtml.test.ts
new file mode 100644
index 0000000..d87d751
--- /dev/null
+++ b/craft/src/components/forms/captcha.toHtml.test.ts
@@ -0,0 +1,49 @@
+import { describe, test, expect } from 'vitest';
+import { ContactForm } from './ContactForm';
+import { SubscribeForm } from './SubscribeForm';
+import { FormContainer } from './FormContainer';
+import { relayFormWiring } from '../../utils/form-relay-wiring';
+
+const cases: [string, any, any][] = [
+  ['ContactForm', (ContactForm as any).toHtml, { fields: [] }],
+  ['SubscribeForm', (SubscribeForm as any).toHtml, {}],
+  ['FormContainer', (FormContainer as any).toHtml, {}],
+];
+const base = { recipientEmail: 'a@b.com', thankYouUrl: '/thx' };
+
+describe.each(cases)('%s captcha marker attribute', (_n, toHtml, extra) => {
+  const run = (p: any) => toHtml({ ...extra, ...base, ...p }, '', 'node1').html as string;
+  test('true emits captcha="1" between id and recipient', () => {
+    expect(run({ captcha: true })).toMatch(/<!--WHP-FORM id="F_[0-9a-z]+" captcha="1" recipient="a@b.com" thankyou="\/thx"-->/);
+  });
+  test('explicit false emits captcha="0"', () => {
+    expect(run({ captcha: false })).toMatch(/<!--WHP-FORM id="F_[0-9a-z]+" captcha="0" recipient=/);
+  });
+  test('undefined (legacy design) is byte-identical to the legacy marker', () => {
+    const html = run({});
+    expect(html).toMatch(/<!--WHP-FORM id="F_[0-9a-z]+" recipient="a@b.com" thankyou="\/thx"-->/);
+    expect(html).not.toContain('captcha');
+    expect(run({ captcha: undefined })).toBe(html);
+  });
+  test('non-boolean junk emits nothing', () => {
+    expect(run({ captcha: 'yes' })).not.toContain('captcha');
+    expect(run({ captcha: 1 })).not.toContain('captcha');
+  });
+  test('no relay (no recipient): no marker at all, even with captcha true', () => {
+    expect(toHtml({ ...extra, captcha: true }, '', 'n').html).not.toContain('WHP-FORM');
+  });
+  test('never emits widget markup (injected at publish)', () => {
+    expect(run({ captcha: true })).not.toMatch(/altcha-widget|challenge\.php|widget\.php/);
+  });
+});
+
+test('webhook marker keeps captcha attr inside the strict-regex attribute zone', () => {
+  const m = relayFormWiring('', '', undefined, 'n', { type: 'webhook', url: 'https://x.y/h' }, true).marker;
+  expect(m).toMatch(/^<!--WHP-FORM id="[^"]+"(?: [a-z]+="[^"]*")* captcha="1" recipient=/);
+});
+
+describe('new forms default to captcha on', () => {
+  test.each([ContactForm, SubscribeForm, FormContainer])('%#', (C: any) => {
+    expect(C.craft.props.captcha).toBe(true);
+  });
+});
diff --git a/craft/src/panels/right/styles/FormStylePanel.tsx b/craft/src/panels/right/styles/FormStylePanel.tsx
index 17380eb..f46aee5 100644
--- a/craft/src/panels/right/styles/FormStylePanel.tsx
+++ b/craft/src/panels/right/styles/FormStylePanel.tsx
@@ -369,6 +369,22 @@ export const FormStylePanel: React.FC<StylePanelProps> = ({ selectedId, nodeProp
           </p>
         </div>
       )}
+      {nodeProps.captcha !== undefined && (
+        <div style={sectionGap}>
+          <label style={{ ...labelStyle, display: 'flex', alignItems: 'center', gap: 6 }}>
+            <input
+              type="checkbox"
+              data-testid="form-captcha"
+              checked={nodeProps.captcha === true}
+              onChange={(e) => setProp('captcha', e.target.checked)}
+            />
+            Spam protection (captcha)
+          </label>
+          <p style={hintStyle}>
+            Adds a privacy-friendly ALTCHA check to the published form (served by the contact-form relay; visitors need JavaScript). Only applies when submissions are sent through the relay.
+          </p>
+        </div>
+      )}
       {nodeProps.thankYouUrl !== undefined && (
         <div style={sectionGap}>
           <label style={labelStyle}>Thank-you page URL (optional)</label>
diff --git a/craft/src/utils/form-relay-wiring.ts b/craft/src/utils/form-relay-wiring.ts
index 98c706f..2970c62 100644
--- a/craft/src/utils/form-relay-wiring.ts
+++ b/craft/src/utils/form-relay-wiring.ts
@@ -82,6 +82,10 @@ export interface RelayWiring {
  *                        the marker/placeholder id deterministically and uniquely --
  *                        see `scopeId` in ./escape. Falls back to a stable hash of the
  *                        recipient/thankYouUrl/fallbackAction when omitted (never random).
+ * @param captcha        ALTCHA captcha intent for the relay (whp: FormRelayRewrite). `true` emits
+ *                        `captcha="1"`, EXPLICIT `false` emits `captcha="0"` (user un-ticked: the
+ *                        relay must clear a stored flag), anything else (undefined/legacy) emits NO
+ *                        attribute, so legacy saved designs stay byte-identical and keep their stored flag.
  * @param destination    optional destination descriptor. Omitted, or `type: 'email'`,
  *                        yields the LEGACY narrow marker byte for byte -- every
  *                        already-published site depends on that shape continuing to
@@ -107,6 +111,7 @@ export function relayFormWiring(
   fallbackAction: string | undefined,
   nodeId?: string,
   destination?: FormDestination,
+  captcha?: boolean,
 ): RelayWiring {
   const destType = allowlist(destination?.type, DESTINATION_TYPES, 'email');
   const isWebhook = destType === 'webhook';
@@ -136,9 +141,12 @@ export function relayFormWiring(
       + markerAttr('authmode', allowlist(destination?.authMode, AUTH_MODES, 'signature'))
     : '';
 
+  const captchaAttr = captcha === true ? markerAttr('captcha', '1')
+    : captcha === false ? markerAttr('captcha', '0') : '';
+
   return {
     useRelay: true,
-    marker: `<!--WHP-FORM id="${fid}"${extraAttrs} recipient="${escapeAttr(recipientEmail || '')}" thankyou="${escapeAttr(thankYouUrl || '')}"-->`,
+    marker: `<!--WHP-FORM id="${fid}"${extraAttrs}${captchaAttr} recipient="${escapeAttr(recipientEmail || '')}" thankyou="${escapeAttr(thankYouUrl || '')}"-->`,
     actionAttr: `__WHP_FORM_ACTION__${fid}__`,
     honeypot: `<input type="text" name="_gotcha" tabindex="-1" autocomplete="off" style="position:absolute;left:-9999px" aria-hidden="true">`,
   };