diff --git a/package-lock.json b/package-lock.json
new file mode 100644
index 0000000000..34682730c1
--- /dev/null
+++ b/package-lock.json
@@ -0,0 +1,22 @@
+{
+  "name": "daily-apps",
+  "lockfileVersion": 3,
+  "requires": true,
+  "packages": {
+    "": {
+      "name": "daily-apps",
+      "dependencies": {
+        "postcss-rem-to-responsive-pixel": "^6.0.2"
+      }
+    },
+    "node_modules/postcss-rem-to-responsive-pixel": {
+      "version": "6.1.0",
+      "resolved": "https://registry.npmjs.org/postcss-rem-to-responsive-pixel/-/postcss-rem-to-responsive-pixel-6.1.0.tgz",
+      "integrity": "sha512-rttz/ThJWKpmhS134NcQCZQBE4CUJIAJAMx9DB0YudIeTH4fNp/hhhjxo14RnGF/OGdBpX9PQw1bnPZ56H0E1Q==",
+      "license": "MIT",
+      "engines": {
+        "node": ">=16.6.0"
+      }
+    }
+  }
+}
diff --git a/packages/shared/src/components/post/freeform/write/WriteFreeformContent.tsx b/packages/shared/src/components/post/freeform/write/WriteFreeformContent.tsx
index f2f0573ba8..fd1243d3ca 100644
--- a/packages/shared/src/components/post/freeform/write/WriteFreeformContent.tsx
+++ b/packages/shared/src/components/post/freeform/write/WriteFreeformContent.tsx
@@ -19,6 +19,7 @@ import type { MergedWriteObject, WriteForm } from '../../../../contexts';
 import { useWritePostContext } from '../../../../contexts';
 import { defaultMarkdownCommands } from '../../../../hooks/input';
 import { WriteFooter } from '../../write';
+import { MAX_POST_TITLE_LENGTH } from '../../../../constants/post';
 
 export const generateWritePostKey = (reference = 'create'): string =>
   `write:post:${reference}`;
@@ -34,7 +35,6 @@ export const checkSavedProperty = (
 const defaultFilename = 'thumbnail.png';
 
 // Shared constants - remember to update them in daily-api
-const MAX_TITLE_LENGTH = 250;
 const MAX_CONTENT_LENGTH = 10_000;
 
 interface WriteFreeformContentProps {
@@ -154,7 +154,7 @@ export function WriteFreeformContent({
           required
           defaultValue={draft?.title ?? fetchedPost?.title}
           onInput={onFormUpdate}
-          maxLength={MAX_TITLE_LENGTH}
+          maxLength={MAX_POST_TITLE_LENGTH}
         />
       </AlertPointer>
       <MarkdownInput
diff --git a/packages/shared/src/components/post/write/ShareLink.tsx b/packages/shared/src/components/post/write/ShareLink.tsx
index f6db6f13a8..846429c059 100644
--- a/packages/shared/src/components/post/write/ShareLink.tsx
+++ b/packages/shared/src/components/post/write/ShareLink.tsx
@@ -15,6 +15,7 @@ import useSourcePostModeration from '../../../hooks/source/useSourcePostModerati
 import type { SourcePostModeration } from '../../../graphql/squads';
 import { usePrompt } from '../../../hooks/usePrompt';
 import { useWritePostContext } from '../../../contexts';
+import { MAX_POST_COMMENTARY_LENGTH } from '../../../constants/post';
 
 interface ShareLinkProps {
   squad?: Squad;
@@ -34,6 +35,7 @@ const confirmSharingAgainPrompt = {
   },
 };
 
+
 export function ShareLink({
   squad,
   className,
@@ -75,6 +77,10 @@ export function ShareLink({
       onSuccess: async () => push(squad?.permalink),
     });
 
+  // Character limit state
+  const commentaryLength = commentary?.length ?? 0;
+  const isCommentaryTooLong = commentaryLength > MAX_POST_COMMENTARY_LENGTH;
+
   const onUpdateSubmit: FormEventHandler<HTMLFormElement> = async (e) => {
     if (!fetchedPost?.id || !squad) {
       return null;
@@ -169,9 +175,16 @@ export function ShareLink({
         enabledCommand={{ mention: true }}
         showMarkdownGuide={false}
         onValueUpdate={setCommentary}
+        maxInputLength={MAX_POST_COMMENTARY_LENGTH}
       />
+      {isCommentaryTooLong && (
+        <p className="text-text-tertiary typo-caption">
+          Maximum length is {MAX_POST_COMMENTARY_LENGTH} characters
+        </p>
+      )}
       <WriteFooter
         isLoading={isPosting || isPostingModeration || isPendingCreation}
+        disabled={isCommentaryTooLong}
       />
     </form>
   );
diff --git a/packages/shared/src/components/post/write/WriteFooter.tsx b/packages/shared/src/components/post/write/WriteFooter.tsx
index 0ace97b77e..6d8043420d 100644
--- a/packages/shared/src/components/post/write/WriteFooter.tsx
+++ b/packages/shared/src/components/post/write/WriteFooter.tsx
@@ -11,12 +11,14 @@ interface WriteFooterProps {
   isLoading?: boolean;
   className?: string;
   isPoll?: boolean;
+  disabled?: boolean;
 }
 
 export function WriteFooter({
   isLoading,
   className,
   isPoll,
+  disabled,
 }: WriteFooterProps): ReactElement {
   const { sidebarRendered } = useSidebarRendered();
   const { shouldShowCta, isEnabled, onToggle, onSubmitted } =
@@ -54,7 +56,7 @@ export function WriteFooter({
           'ml-auto hidden w-full tablet:mt-0 tablet:w-32 laptop:flex',
           shouldShowCta && 'mt-6',
         )}
-        disabled={isLoading}
+        disabled={isLoading || disabled}
         loading={isLoading}
         onClick={onSubmitted}
       >
diff --git a/packages/shared/src/constants/README.md b/packages/shared/src/constants/README.md
new file mode 100644
index 0000000000..8a7e80362e
--- /dev/null
+++ b/packages/shared/src/constants/README.md
@@ -0,0 +1,38 @@
+# Post Constants
+
+Single source of truth for post-related character limits.
+
+## Constants
+
+### `MAX_POST_TITLE_LENGTH = 250`
+
+Maximum characters for post titles.
+
+**Used in:** `WriteFreeformContent.tsx` (title field)
+
+```typescript
+import { MAX_POST_TITLE_LENGTH } from '../../../../constants/post';
+
+<TextField maxLength={MAX_POST_TITLE_LENGTH} />
+```
+
+### `MAX_POST_COMMENTARY_LENGTH = 250`
+
+Maximum characters for link commentary/descriptions.
+
+**Used in:** `ShareLink.tsx` (commentary field + validation)
+
+```typescript
+import { MAX_POST_COMMENTARY_LENGTH } from '../../../constants/post';
+
+// Validation
+if (commentary.length > MAX_POST_COMMENTARY_LENGTH) return null;
+
+// Component
+<MarkdownInput maxInputLength={MAX_POST_COMMENTARY_LENGTH} />
+```
+
+## Notes
+
+- **Backend sync required:** Keep these in sync with `daily-api` validation
+- **Naming pattern:** `MAX_POST_[FIELD]_LENGTH`
diff --git a/packages/shared/src/constants/post.ts b/packages/shared/src/constants/post.ts
new file mode 100644
index 0000000000..494543ebe2
--- /dev/null
+++ b/packages/shared/src/constants/post.ts
@@ -0,0 +1,2 @@
+export const MAX_POST_TITLE_LENGTH = 250;
+export const MAX_POST_COMMENTARY_LENGTH = 250;