diff --git a/app/javascript/mastodon/features/compose/components/compose_form.jsx b/app/javascript/mastodon/features/compose/components/compose_form.jsx
index 468125afb..2cd88aab4 100644
--- a/app/javascript/mastodon/features/compose/components/compose_form.jsx
+++ b/app/javascript/mastodon/features/compose/components/compose_form.jsx
@@ -10,6 +10,8 @@ import ImmutablePureComponent from 'react-immutable-pure-component';
 
 import { length } from 'stringz';
 
+import { missingAltTextModal } from 'mastodon/initial_state';
+
 import AutosuggestInput from '../../../components/autosuggest_input';
 import AutosuggestTextarea from '../../../components/autosuggest_textarea';
 import { Button } from '../../../components/button';
@@ -65,6 +67,7 @@ class ComposeForm extends ImmutablePureComponent {
     autoFocus: PropTypes.bool,
     withoutNavigation: PropTypes.bool,
     anyMedia: PropTypes.bool,
+    missingAltText: PropTypes.bool,
     isInReply: PropTypes.bool,
     singleColumn: PropTypes.bool,
     lang: PropTypes.string,
@@ -117,7 +120,7 @@ class ComposeForm extends ImmutablePureComponent {
       return;
     }
 
-    this.props.onSubmit();
+    this.props.onSubmit(missingAltTextModal && this.props.missingAltText);
 
     if (e) {
       e.preventDefault();
diff --git a/app/javascript/mastodon/features/compose/containers/compose_form_container.js b/app/javascript/mastodon/features/compose/containers/compose_form_container.js
index bda2edba6..15ccabf74 100644
--- a/app/javascript/mastodon/features/compose/containers/compose_form_container.js
+++ b/app/javascript/mastodon/features/compose/containers/compose_form_container.js
@@ -9,7 +9,9 @@ import {
   changeComposeSpoilerText,
   insertEmojiCompose,
   uploadCompose,
-} from '../../../actions/compose';
+} from 'mastodon/actions/compose';
+import { openModal } from 'mastodon/actions/modal';
+
 import ComposeForm from '../components/compose_form';
 
 const mapStateToProps = state => ({
@@ -26,6 +28,7 @@ const mapStateToProps = state => ({
   isChangingUpload: state.getIn(['compose', 'is_changing_upload']),
   isUploading: state.getIn(['compose', 'is_uploading']),
   anyMedia: state.getIn(['compose', 'media_attachments']).size > 0,
+  missingAltText: state.getIn(['compose', 'media_attachments']).some(media => ['image', 'gifv'].includes(media.get('type')) && (media.get('description') ?? '').length === 0),
   isInReply: state.getIn(['compose', 'in_reply_to']) !== null,
   lang: state.getIn(['compose', 'language']),
   maxChars: state.getIn(['server', 'server', 'configuration', 'statuses', 'max_characters'], 500),
@@ -37,8 +40,15 @@ const mapDispatchToProps = (dispatch) => ({
     dispatch(changeCompose(text));
   },
 
-  onSubmit () {
-    dispatch(submitCompose());
+  onSubmit (missingAltText) {
+    if (missingAltText) {
+      dispatch(openModal({
+        modalType: 'CONFIRM_MISSING_ALT_TEXT',
+        modalProps: {},
+      }));
+    } else {
+      dispatch(submitCompose());
+    }
   },
 
   onClearSuggestions () {
diff --git a/app/javascript/mastodon/features/ui/components/confirmation_modals/confirmation_modal.tsx b/app/javascript/mastodon/features/ui/components/confirmation_modals/confirmation_modal.tsx
index ab567c697..929b1a240 100644
--- a/app/javascript/mastodon/features/ui/components/confirmation_modals/confirmation_modal.tsx
+++ b/app/javascript/mastodon/features/ui/components/confirmation_modals/confirmation_modal.tsx
@@ -56,14 +56,6 @@ export const ConfirmationModal: React.FC<
 
       <div className='safety-action-modal__bottom'>
         <div className='safety-action-modal__actions'>
-          {secondary && (
-            <>
-              <Button onClick={handleSecondary}>{secondary}</Button>
-
-              <div className='spacer' />
-            </>
-          )}
-
           <button onClick={handleCancel} className='link-button'>
             <FormattedMessage
               id='confirmation_modal.cancel'
@@ -71,6 +63,15 @@ export const ConfirmationModal: React.FC<
             />
           </button>
 
+          {secondary && (
+            <>
+              <div className='spacer' />
+              <button onClick={handleSecondary} className='link-button'>
+                {secondary}
+              </button>
+            </>
+          )}
+
           {/* eslint-disable-next-line jsx-a11y/no-autofocus -- we are in a modal and thus autofocusing is justified */}
           <Button onClick={handleClick} autoFocus>
             {confirm}
diff --git a/app/javascript/mastodon/features/ui/components/confirmation_modals/index.ts b/app/javascript/mastodon/features/ui/components/confirmation_modals/index.ts
index 16478d0d1..4893fb096 100644
--- a/app/javascript/mastodon/features/ui/components/confirmation_modals/index.ts
+++ b/app/javascript/mastodon/features/ui/components/confirmation_modals/index.ts
@@ -7,3 +7,4 @@ export { ConfirmUnfollowModal } from './unfollow';
 export { ConfirmClearNotificationsModal } from './clear_notifications';
 export { ConfirmLogOutModal } from './log_out';
 export { ConfirmFollowToListModal } from './follow_to_list';
+export { ConfirmMissingAltTextModal } from './missing_alt_text';
diff --git a/app/javascript/mastodon/features/ui/components/confirmation_modals/missing_alt_text.tsx b/app/javascript/mastodon/features/ui/components/confirmation_modals/missing_alt_text.tsx
new file mode 100644
index 000000000..057a1191d
--- /dev/null
+++ b/app/javascript/mastodon/features/ui/components/confirmation_modals/missing_alt_text.tsx
@@ -0,0 +1,81 @@
+import { useCallback } from 'react';
+
+import { defineMessages, useIntl } from 'react-intl';
+
+import type { Map as ImmutableMap, List as ImmutableList } from 'immutable';
+
+import { submitCompose } from 'mastodon/actions/compose';
+import { openModal } from 'mastodon/actions/modal';
+import type { MediaAttachment } from 'mastodon/models/media_attachment';
+import { useAppDispatch, useAppSelector } from 'mastodon/store';
+
+import type { BaseConfirmationModalProps } from './confirmation_modal';
+import { ConfirmationModal } from './confirmation_modal';
+
+const messages = defineMessages({
+  title: {
+    id: 'confirmations.missing_alt_text.title',
+    defaultMessage: 'Add alt text?',
+  },
+  confirm: {
+    id: 'confirmations.missing_alt_text.confirm',
+    defaultMessage: 'Add alt text',
+  },
+  message: {
+    id: 'confirmations.missing_alt_text.message',
+    defaultMessage:
+      'Your post contains media without alt text. Adding descriptions helps make your content accessible to more people.',
+  },
+  secondary: {
+    id: 'confirmations.missing_alt_text.secondary',
+    defaultMessage: 'Post anyway',
+  },
+});
+
+export const ConfirmMissingAltTextModal: React.FC<
+  BaseConfirmationModalProps
+> = ({ onClose }) => {
+  const intl = useIntl();
+  const dispatch = useAppDispatch();
+  const mediaId = useAppSelector(
+    (state) =>
+      (
+        (state.compose as ImmutableMap<string, unknown>).get(
+          'media_attachments',
+        ) as ImmutableList<MediaAttachment>
+      )
+        .find(
+          (media) =>
+            ['image', 'gifv'].includes(media.get('type') as string) &&
+            ((media.get('description') ?? '') as string).length === 0,
+        )
+        ?.get('id') as string,
+  );
+
+  const handleConfirm = useCallback(() => {
+    dispatch(
+      openModal({
+        modalType: 'FOCAL_POINT',
+        modalProps: {
+          mediaId,
+        },
+      }),
+    );
+  }, [dispatch, mediaId]);
+
+  const handleSecondary = useCallback(() => {
+    dispatch(submitCompose());
+  }, [dispatch]);
+
+  return (
+    <ConfirmationModal
+      title={intl.formatMessage(messages.title)}
+      message={intl.formatMessage(messages.message)}
+      confirm={intl.formatMessage(messages.confirm)}
+      secondary={intl.formatMessage(messages.secondary)}
+      onConfirm={handleConfirm}
+      onSecondary={handleSecondary}
+      onClose={onClose}
+    />
+  );
+};
diff --git a/app/javascript/mastodon/features/ui/components/modal_root.jsx b/app/javascript/mastodon/features/ui/components/modal_root.jsx
index 5e44b53fb..cb1e499db 100644
--- a/app/javascript/mastodon/features/ui/components/modal_root.jsx
+++ b/app/javascript/mastodon/features/ui/components/modal_root.jsx
@@ -37,6 +37,7 @@ import {
   ConfirmClearNotificationsModal,
   ConfirmLogOutModal,
   ConfirmFollowToListModal,
+  ConfirmMissingAltTextModal,
 } from './confirmation_modals';
 import ImageModal from './image_modal';
 import MediaModal from './media_modal';
@@ -58,6 +59,7 @@ export const MODAL_COMPONENTS = {
   'CONFIRM_CLEAR_NOTIFICATIONS': () => Promise.resolve({ default: ConfirmClearNotificationsModal }),
   'CONFIRM_LOG_OUT': () => Promise.resolve({ default: ConfirmLogOutModal }),
   'CONFIRM_FOLLOW_TO_LIST': () => Promise.resolve({ default: ConfirmFollowToListModal }),
+  'CONFIRM_MISSING_ALT_TEXT': () => Promise.resolve({ default: ConfirmMissingAltTextModal }),
   'MUTE': MuteModal,
   'BLOCK': BlockModal,
   'DOMAIN_BLOCK': DomainBlockModal,
diff --git a/app/javascript/mastodon/initial_state.js b/app/javascript/mastodon/initial_state.js
index 40942eb7e..093422ac8 100644
--- a/app/javascript/mastodon/initial_state.js
+++ b/app/javascript/mastodon/initial_state.js
@@ -14,6 +14,7 @@
  * @property {string} admin
  * @property {boolean=} boost_modal
  * @property {boolean=} delete_modal
+ * @property {boolean=} missing_alt_text_modal
  * @property {boolean=} disable_swiping
  * @property {boolean=} disable_hover_cards
  * @property {string=} disabled_account_id
@@ -88,6 +89,7 @@ export const activityApiEnabled = getMeta('activity_api_enabled');
 export const autoPlayGif = getMeta('auto_play_gif');
 export const boostModal = getMeta('boost_modal');
 export const deleteModal = getMeta('delete_modal');
+export const missingAltTextModal = getMeta('missing_alt_text_modal');
 export const disableSwiping = getMeta('disable_swiping');
 export const disableHoverCards = getMeta('disable_hover_cards');
 export const disabledAccountId = getMeta('disabled_account_id');
diff --git a/app/javascript/mastodon/locales/en.json b/app/javascript/mastodon/locales/en.json
index a2dedd22d..93e485f09 100644
--- a/app/javascript/mastodon/locales/en.json
+++ b/app/javascript/mastodon/locales/en.json
@@ -218,6 +218,10 @@
   "confirmations.logout.confirm": "Log out",
   "confirmations.logout.message": "Are you sure you want to log out?",
   "confirmations.logout.title": "Log out?",
+  "confirmations.missing_alt_text.confirm": "Add alt text",
+  "confirmations.missing_alt_text.message": "Your post contains media without alt text. Adding descriptions helps make your content accessible to more people.",
+  "confirmations.missing_alt_text.secondary": "Post anyway",
+  "confirmations.missing_alt_text.title": "Add alt text?",
   "confirmations.mute.confirm": "Mute",
   "confirmations.redraft.confirm": "Delete & redraft",
   "confirmations.redraft.message": "Are you sure you want to delete this post and re-draft it? Favorites and boosts will be lost, and replies to the original post will be orphaned.",
diff --git a/app/models/user_settings.rb b/app/models/user_settings.rb
index 7db14407a..4151a9afe 100644
--- a/app/models/user_settings.rb
+++ b/app/models/user_settings.rb
@@ -29,6 +29,7 @@ class UserSettings
     setting :disable_hover_cards, default: false
     setting :delete_modal, default: true
     setting :reblog_modal, default: false
+    setting :missing_alt_text_modal, default: true
     setting :reduce_motion, default: false
     setting :expand_content_warnings, default: false
     setting :display_media, default: 'default', in: %w(default show_all hide_all)
diff --git a/app/serializers/initial_state_serializer.rb b/app/serializers/initial_state_serializer.rb
index 5778bcc60..0ad06d22c 100644
--- a/app/serializers/initial_state_serializer.rb
+++ b/app/serializers/initial_state_serializer.rb
@@ -12,13 +12,14 @@ class InitialStateSerializer < ActiveModel::Serializer
   has_one :push_subscription, serializer: REST::WebPushSubscriptionSerializer
   has_one :role, serializer: REST::RoleSerializer
 
-  def meta
+  def meta # rubocop:disable Metrics/AbcSize
     store = default_meta_store
 
     if object.current_account
       store[:me]                = object.current_account.id.to_s
       store[:boost_modal]       = object_account_user.setting_boost_modal
       store[:delete_modal]      = object_account_user.setting_delete_modal
+      store[:missing_alt_text_modal] = object_account_user.settings['web.missing_alt_text_modal']
       store[:auto_play_gif]     = object_account_user.setting_auto_play_gif
       store[:display_media]     = object_account_user.setting_display_media
       store[:expand_spoilers]   = object_account_user.setting_expand_spoilers
diff --git a/app/views/settings/preferences/appearance/show.html.haml b/app/views/settings/preferences/appearance/show.html.haml
index 08cfea5a4..8fd7a85de 100644
--- a/app/views/settings/preferences/appearance/show.html.haml
+++ b/app/views/settings/preferences/appearance/show.html.haml
@@ -71,6 +71,7 @@
     .fields-group
       = ff.input :'web.reblog_modal', wrapper: :with_label, label: I18n.t('simple_form.labels.defaults.setting_boost_modal')
       = ff.input :'web.delete_modal', wrapper: :with_label, label: I18n.t('simple_form.labels.defaults.setting_delete_modal')
+      = ff.input :'web.missing_alt_text_modal', wrapper: :with_label, label: I18n.t('simple_form.labels.defaults.setting_missing_alt_text_modal')
 
     %h4= t 'appearance.sensitive_content'
 
diff --git a/config/locales/simple_form.en.yml b/config/locales/simple_form.en.yml
index 696ccd35d..edf0a29a3 100644
--- a/config/locales/simple_form.en.yml
+++ b/config/locales/simple_form.en.yml
@@ -233,6 +233,7 @@ en:
         setting_display_media_show_all: Show all
         setting_expand_spoilers: Always expand posts marked with content warnings
         setting_hide_network: Hide your social graph
+        setting_missing_alt_text_modal: Show confirmation dialog before posting media without alt text
         setting_reduce_motion: Reduce motion in animations
         setting_system_font_ui: Use system's default font
         setting_system_scrollbars_ui: Use system's default scrollbar