diff --git a/apps/site/platform/messages/en.ts b/apps/site/platform/messages/en.ts
index 15b48136..645d8129 100644
--- a/apps/site/platform/messages/en.ts
+++ b/apps/site/platform/messages/en.ts
@@ -12,12 +12,16 @@ export const en = {
     intro:
       "Members get LVBT's updates, invitations to events and a say in what we work on. It's free.",
     emailLabel: 'Email address',
+    emailHint: "We'll send your welcome email and LVBT updates here, about 1–2 times a week.",
     givenNameLabel: 'First name',
+    givenNameHint: "We'll use this to greet you in your welcome email.",
     givenNameError: 'Enter your first name',
     familyNameLabel: 'Last name (optional)',
+    familyNameHint: 'Your account will show this with your first name.',
     phoneLabel: 'Phone number (optional)',
     phoneHint: 'Only for questions about your membership. LVBT updates come by email.',
     interestsHeading: 'What are you interested in? (optional)',
+    interestsHint: "We'll use your choices to suggest events and ways to help.",
     interestEvents: 'Coming to events',
     interestMeetings: 'Speaking up at public meetings',
     interestVolunteering: 'Volunteering on a team',
@@ -25,7 +29,7 @@ export const en = {
     discordUsernameLabel: 'Discord username (optional)',
     discordUsernameHint: 'We can use this later to give you the right roles in our server.',
     transportHeading: 'What do you own for getting around? (optional)',
-    transportHint: 'Select all that apply, or leave this blank.',
+    transportHint: 'This helps us understand how members get around. You can skip it.',
     transportCar: 'Car',
     micromobilityBike: 'Bike (traditional)',
     micromobilityEbike: 'E-bike',
diff --git a/apps/site/public/scripts/join-steps.js b/apps/site/public/scripts/join-steps.js
index 9ee8cb23..44d133ae 100644
--- a/apps/site/public/scripts/join-steps.js
+++ b/apps/site/public/scripts/join-steps.js
@@ -16,6 +16,48 @@
     });
   }
 
+  function validateBasicFields({ form, summary, email, givenName, phone, consent }) {
+    function setFieldError(field, invalid) {
+      const error = form.querySelector(`[data-error-for="${field.id}"]`);
+      const item = summary.querySelector(`[data-summary-for="${field.id}"]`);
+      if (!error || !item) return;
+      error.hidden = !invalid;
+      item.hidden = !invalid;
+      field.toggleAttribute('aria-invalid', invalid);
+      const describedBy = (field.getAttribute('aria-describedby') || '')
+        .split(/\s+/)
+        .filter((id) => id && id !== error.id);
+      if (invalid) describedBy.unshift(error.id);
+      if (describedBy.length) field.setAttribute('aria-describedby', describedBy.join(' '));
+      else field.removeAttribute('aria-describedby');
+      summary.hidden = !summary.querySelector('[data-summary-for]:not([hidden])');
+    }
+
+    for (const field of [email, givenName, phone, consent]) {
+      field.addEventListener(field === consent ? 'change' : 'input', () =>
+        setFieldError(field, false),
+      );
+    }
+
+    return () => {
+      const digits = phone.value.replace(/\D/g, '');
+      const invalid = [
+        [email, !/^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email.value.trim())],
+        [givenName, !givenName.value.trim()],
+        [
+          phone,
+          Boolean(phone.value.trim()) &&
+            !(digits.length === 10 || (digits.length === 11 && digits.startsWith('1'))),
+        ],
+        [consent, !consent.checked],
+      ];
+      invalid.forEach(([field, failed]) => setFieldError(field, failed));
+      if (!invalid.some(([, failed]) => failed)) return true;
+      summary.focus();
+      return false;
+    };
+  }
+
   function run() {
     const form = document.querySelector('form[action="/join/member/"][data-enhance]');
     const progress = document.querySelector('[data-join-progress]');
@@ -27,7 +69,9 @@
     const backButton = form.querySelector('[data-join-back]');
     const email = form.querySelector('[name="email"]');
     const givenName = form.querySelector('[name="given_name"]');
+    const phone = form.querySelector('[name="phone"]');
     const consent = form.querySelector('[name="consent"]');
+    const errorSummary = document.querySelector('[data-error-summary]');
     const items = progress.querySelectorAll('li');
     const basicHeading = document.querySelector('[data-join-heading-basic]');
     const interestsHeading = document.querySelector('[data-join-heading-interests]');
@@ -40,7 +84,9 @@
         backButton,
         email,
         givenName,
+        phone,
         consent,
+        errorSummary,
         basicHeading,
         interestsHeading,
         intro,
@@ -52,6 +98,14 @@
     progress.style.display = '';
     continueButton.style.display = '';
     backButton.style.display = '';
+    const basicFieldsValid = validateBasicFields({
+      form,
+      summary: errorSummary,
+      email,
+      givenName,
+      phone,
+      consent,
+    });
 
     function show(step) {
       first.hidden = step !== 1;
@@ -67,16 +121,10 @@
     }
 
     function continueToInterests() {
-      if (!email.reportValidity()) return;
-      if (!givenName.value.trim()) givenName.setCustomValidity('Enter your first name');
-      else givenName.setCustomValidity('');
-      if (!givenName.reportValidity()) return;
-      if (!consent.reportValidity()) return;
-      show(2);
+      if (basicFieldsValid()) show(2);
     }
 
     second.hidden = true;
-    givenName.addEventListener('input', () => givenName.setCustomValidity(''));
     continueButton.addEventListener('click', continueToInterests);
     backButton.addEventListener('click', () => show(1));
     form.addEventListener(
diff --git a/apps/site/src/components/join/JoinForm.astro b/apps/site/src/components/join/JoinForm.astro
index 97d94ea6..ef5d7b55 100644
--- a/apps/site/src/components/join/JoinForm.astro
+++ b/apps/site/src/components/join/JoinForm.astro
@@ -42,6 +42,7 @@ const { action } = Astro.props;
     <TextField
       name="email"
       label={t('join.emailLabel')}
+      hint={t('join.emailHint')}
       type="email"
       autocomplete="email"
       required
@@ -52,11 +53,17 @@ const { action } = Astro.props;
       <TextField
         name="given_name"
         label={t('join.givenNameLabel')}
+        hint={t('join.givenNameHint')}
         autocomplete="given-name"
         required
         error={t('join.givenNameError')}
       />
-      <TextField name="family_name" label={t('join.familyNameLabel')} autocomplete="family-name" />
+      <TextField
+        name="family_name"
+        label={t('join.familyNameLabel')}
+        hint={t('join.familyNameHint')}
+        autocomplete="family-name"
+      />
     </div>
 
     <TextField
@@ -97,6 +104,7 @@ const { action } = Astro.props;
     <ChoiceGroup
       name="interests"
       legend={t('join.interestsHeading')}
+      hint={t('join.interestsHint')}
       type="checkbox"
       cards
       options={[
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 7eefbbb5..943e0eb1 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -122,6 +122,7 @@ catalogs:
       version: 4.5.4
 
 overrides:
+  devalue: 5.9.4
   sharp: 0.35.4
   smol-toml: 1.8.0
   svgo: 4.1.0
@@ -2674,8 +2675,8 @@ packages:
     resolution: {integrity: sha512-Btj2BOOO83o3WyH59e8MgXsxEQVcarkUOpEYrubB0urwnN10yQ364rsiByU11nZlqWYZm05i/of7io4mzihBtQ==}
     engines: {node: '>=8'}
 
-  devalue@5.8.1:
-    resolution: {integrity: sha512-4CXDYRBGqN+57wVJkuXBYmpAVUSg3L6JAQa/DFqm238G73E1wuyc/JhGQJzN7vUf/CMphYau2zXbfWzDR5aTEw==}
+  devalue@5.9.4:
+    resolution: {integrity: sha512-sPAT4pztbu6586/hrhOnMKS17IJrvg12mXiSPSS3W5qDeN2RGgvZ0diZCm31dBbnevfVmujNO3IM2wrS4Y2Rhg==}
 
   devlop@1.1.0:
     resolution: {integrity: sha512-RWmIqhcFf1lRYBvNmr7qTNuyCt/7/ns2jbpp1+PalgE/rDQcBT0fioSMUpJ93irlUhC5hrg4cYqe6U+0ImW0rA==}
@@ -7798,7 +7799,7 @@ snapshots:
       clsx: 2.1.1
       common-ancestor-path: 2.0.0
       cookie: 2.0.1
-      devalue: 5.8.1
+      devalue: 5.9.4
       diff: 9.0.0
       dset: 3.1.4
       es-module-lexer: 2.1.0
@@ -8430,7 +8431,7 @@ snapshots:
 
   detect-libc@2.1.2: {}
 
-  devalue@5.8.1: {}
+  devalue@5.9.4: {}
 
   devlop@1.1.0:
     dependencies:
diff --git a/pnpm-workspace.yaml b/pnpm-workspace.yaml
index 68a6eea2..5814738e 100644
--- a/pnpm-workspace.yaml
+++ b/pnpm-workspace.yaml
@@ -24,6 +24,7 @@ packageExtensions:
 # Temporary transitive pins for published security fixes not yet selected by
 # their direct dependents.
 overrides:
+  devalue: 5.9.4
   sharp: 0.35.4
   smol-toml: 1.8.0
   svgo: 4.1.0