diff --git a/src/view/com/composer/text-input/TextInput.web.tsx b/src/view/com/composer/text-input/TextInput.web.tsx
index 7eea904ab0..d116b6b230 100644
--- a/src/view/com/composer/text-input/TextInput.web.tsx
+++ b/src/view/com/composer/text-input/TextInput.web.tsx
@@ -17,6 +17,7 @@ import {useColorSchemeStyle} from 'lib/hooks/useColorSchemeStyle'
 import {isUriImage, blobToDataUri} from 'lib/media/util'
 import {Emoji} from './web/EmojiPicker.web'
 import {LinkDecorator} from './web/LinkDecorator'
+import {TagDecorator} from './web/TagDecorator'
 
 export interface TextInputRef {
   focus: () => void
@@ -71,6 +72,7 @@ export const TextInput = React.forwardRef(function TextInputImpl(
       extensions: [
         Document,
         LinkDecorator,
+        TagDecorator,
         Mention.configure({
           HTMLAttributes: {
             class: 'mention',
diff --git a/src/view/com/composer/text-input/web/TagDecorator.ts b/src/view/com/composer/text-input/web/TagDecorator.ts
new file mode 100644
index 0000000000..39fe521ca6
--- /dev/null
+++ b/src/view/com/composer/text-input/web/TagDecorator.ts
@@ -0,0 +1,80 @@
+/**
+ * TipTap is a stateful rich-text editor, which is extremely useful
+ * when you _want_ it to be stateful formatting such as bold and italics.
+ *
+ * However we also use "stateless" behaviors, specifically for URLs
+ * where the text itself drives the formatting.
+ *
+ * This plugin uses a regex to detect URIs and then applies
+ * link decorations (a <span> with the "autolink") class. That avoids
+ * adding any stateful formatting to TipTap's document model.
+ *
+ * We then run the URI detection again when constructing the
+ * RichText object from TipTap's output and merge their features into
+ * the facet-set.
+ */
+
+import {Mark} from '@tiptap/core'
+import {Plugin, PluginKey} from '@tiptap/pm/state'
+import {findChildren} from '@tiptap/core'
+import {Node as ProsemirrorNode} from '@tiptap/pm/model'
+import {Decoration, DecorationSet} from '@tiptap/pm/view'
+
+const TAG_REGEX = /(?:^|\s)(#[^\d\s]\S*)(?=\s)?/g
+
+function getDecorations(doc: ProsemirrorNode) {
+  const decorations: Decoration[] = []
+
+  findChildren(doc, node => node.type.name === 'paragraph').forEach(
+    paragraphNode => {
+      const textContent = paragraphNode.node.textContent
+
+      let match
+      while ((match = TAG_REGEX.exec(textContent))) {
+        const [, m] = match
+        const tag = m.trim().replace(/\p{P}+$/gu, '')
+        const from = match.index + 1
+        const to = from + tag.length + 1
+        decorations.push(
+          Decoration.inline(paragraphNode.pos + from, paragraphNode.pos + to, {
+            class: 'autolink',
+          }),
+        )
+      }
+    },
+  )
+
+  return DecorationSet.create(doc, decorations)
+}
+
+const tagDecoratorPlugin: Plugin = new Plugin({
+  key: new PluginKey('link-decorator'),
+
+  state: {
+    init: (_, {doc}) => getDecorations(doc),
+    apply: (transaction, decorationSet) => {
+      if (transaction.docChanged) {
+        return getDecorations(transaction.doc)
+      }
+      return decorationSet.map(transaction.mapping, transaction.doc)
+    },
+  },
+
+  props: {
+    decorations(state) {
+      return tagDecoratorPlugin.getState(state)
+    },
+  },
+})
+
+export const TagDecorator = Mark.create({
+  name: 'tag-decorator',
+  priority: 1000,
+  keepOnSplit: false,
+  inclusive() {
+    return true
+  },
+  addProseMirrorPlugins() {
+    return [tagDecoratorPlugin]
+  },
+})