diff --git a/README.md b/README.md
index 1070757..bd7dca3 100644
--- a/README.md
+++ b/README.md
@@ -233,6 +233,8 @@ After logging in, open <http://localhost:8000/profile>, enter the Mastodon insta
 
 `LINKLOG_PUBLIC_URL` must be the URL users can reach for the OAuth callback. For local development it can remain `http://localhost:8000`; for a deployment it must be the public LinkLog URL. Existing manually entered access tokens remain compatible with the plugin configuration API.
 
+LinkLog caches the OAuth application credentials per Mastodon server in the persistent SQLite `app_settings` table, so subsequent connections do not register a new application on every attempt. If the server rate-limits application registration, the profile page reports the upstream `429` response and the user can retry after the server's cooldown.
+
 Enable the plugin from the admin API or the admin page. New links are saved first and then posted to the configured instance at `/api/v1/statuses`. A Mastodon network failure does not undo the saved link.
 
 ## Useful API Calls
diff --git a/backend/app/api/mastodon.py b/backend/app/api/mastodon.py
index d2bc6a3..9a1d772 100644
--- a/backend/app/api/mastodon.py
+++ b/backend/app/api/mastodon.py
@@ -2,6 +2,7 @@
 ## SPDX-License-Identifier: GPL-3.0-or-later
 
 from urllib.parse import quote
+from urllib.error import HTTPError
 
 from fastapi import APIRouter, Depends, HTTPException
 from fastapi.responses import RedirectResponse
@@ -17,6 +18,14 @@ router = APIRouter()
 def oauth_start(instance: str = 'mastodon.social', user: dict = Depends(get_current_user)):
     try:
         authorization_url = start_authorization(user['id'], instance)
+    except HTTPError as error:
+        retry_after = error.headers.get('Retry-After') if error.headers else None
+        headers = {'Retry-After': retry_after} if retry_after else None
+        raise HTTPException(
+            status_code=error.code,
+            detail=f'Mastodon returned HTTP {error.code} while registering LinkLog. Try again later.',
+            headers=headers,
+        ) from error
     except Exception as error:
         raise HTTPException(status_code=502, detail=f'Could not register with Mastodon: {error}') from error
     return {'authorization_url': authorization_url}
diff --git a/backend/app/services/mastodon_oauth.py b/backend/app/services/mastodon_oauth.py
index bcc9442..7a2dcd9 100644
--- a/backend/app/services/mastodon_oauth.py
+++ b/backend/app/services/mastodon_oauth.py
@@ -6,6 +6,7 @@ from hashlib import sha256
 import json
 from secrets import token_urlsafe
 from urllib.parse import urlencode
+from urllib.error import HTTPError
 from urllib.request import Request, urlopen
 from uuid import uuid4
 
@@ -34,12 +35,24 @@ def post_form(url: str, values: dict) -> dict:
 def start_authorization(user_id: str, instance: str) -> str:
     instance = normalize_instance(instance)
     redirect_uri = f'{settings.public_url}/api/mastodon/oauth/callback'
-    app = post_form(f'{instance}/api/v1/apps', {
-        'client_name': settings.mastodon_client_name,
-        'redirect_uris': redirect_uri,
-        'scopes': 'read:accounts write:statuses',
-        'website': settings.public_url,
-    })
+    setting_name = f'mastodon_app:{instance}'
+    with get_connection() as conn:
+        row = conn.execute('SELECT value FROM app_settings WHERE name = ?', (setting_name,)).fetchone()
+    app = json.loads(row['value']) if row else None
+    if not app:
+        app = post_form(f'{instance}/api/v1/apps', {
+            'client_name': settings.mastodon_client_name,
+            'redirect_uris': redirect_uri,
+            'scopes': 'read:accounts write:statuses',
+            'website': settings.public_url,
+        })
+        with get_connection() as conn:
+            conn.execute(
+                '''INSERT INTO app_settings (name, value, updated_at) VALUES (?, ?, CURRENT_TIMESTAMP)
+                   ON CONFLICT(name) DO UPDATE SET value = excluded.value, updated_at = CURRENT_TIMESTAMP''',
+                (setting_name, json.dumps(app)),
+            )
+            conn.commit()
     state = token_urlsafe(32)
     expires_at = datetime.now(timezone.utc) + timedelta(minutes=settings.mastodon_oauth_expiry_minutes)
     with get_connection() as conn:
diff --git a/frontend/static/profile.js b/frontend/static/profile.js
index d578ef3..2de2216 100644
--- a/frontend/static/profile.js
+++ b/frontend/static/profile.js
@@ -111,7 +111,7 @@ mastodonConnectButton.addEventListener('click', async () => {
     setStatus('#mastodon-status', `Authorizing with ${instance}...`);
     const response = await fetch(`/api/mastodon/oauth/start?instance=${encodeURIComponent(instance)}`, {headers: authHeaders()});
     const result = await response.json();
-    if (!response.ok || !result.authorization_url) throw new Error(result.error || 'Could not start Mastodon authorization.');
+    if (!response.ok || !result.authorization_url) throw new Error(result.detail || result.error || 'Could not start Mastodon authorization.');
     window.location.assign(result.authorization_url);
   } catch (error) {
     setStatus('#mastodon-status', error.message, true);