diff --git a/bookmarks/api/routes.py b/bookmarks/api/routes.py
index 562d007..649d581 100644
--- a/bookmarks/api/routes.py
+++ b/bookmarks/api/routes.py
@@ -27,6 +27,7 @@ from bookmarks.models import (
     BookmarkBundle,
 )
 from bookmarks.services import assets, bookmarks, bundles, auto_tagging, website_loader
+from bookmarks.utils import normalize_url
 from bookmarks.type_defs import HttpRequest
 from bookmarks.views import access
 
@@ -107,7 +108,10 @@ class BookmarkViewSet(
     def check(self, request: HttpRequest):
         url = request.GET.get("url")
         ignore_cache = request.GET.get("ignore_cache", False) in ["true"]
-        bookmark = Bookmark.objects.filter(owner=request.user, url=url).first()
+        normalized_url = normalize_url(url)
+        bookmark = Bookmark.objects.filter(
+            owner=request.user, url_normalized=normalized_url
+        ).first()
         existing_bookmark_data = (
             self.get_serializer(bookmark).data if bookmark else None
         )
@@ -151,7 +155,10 @@ class BookmarkViewSet(
                 status=status.HTTP_400_BAD_REQUEST,
             )
 
-        bookmark = Bookmark.objects.filter(owner=request.user, url=url).first()
+        normalized_url = normalize_url(url)
+        bookmark = Bookmark.objects.filter(
+            owner=request.user, url_normalized=normalized_url
+        ).first()
 
         if not bookmark:
             bookmark = Bookmark(url=url)
diff --git a/bookmarks/forms.py b/bookmarks/forms.py
index 5aa3efc..c571d0f 100644
--- a/bookmarks/forms.py
+++ b/bookmarks/forms.py
@@ -5,6 +5,7 @@ from bookmarks.models import Bookmark, build_tag_string
 from bookmarks.validators import BookmarkURLValidator
 from bookmarks.type_defs import HttpRequest
 from bookmarks.services.bookmarks import create_bookmark, update_bookmark
+from bookmarks.utils import normalize_url
 
 
 class CustomErrorList(ErrorList):
@@ -85,8 +86,11 @@ class BookmarkForm(forms.ModelForm):
         # raise a validation error in that case.
         url = self.cleaned_data["url"]
         if self.instance.pk:
+            normalized_url = normalize_url(url)
             is_duplicate = (
-                Bookmark.objects.filter(owner=self.instance.owner, url=url)
+                Bookmark.objects.filter(
+                    owner=self.instance.owner, url_normalized=normalized_url
+                )
                 .exclude(pk=self.instance.pk)
                 .exists()
             )
diff --git a/bookmarks/migrations/0046_add_url_normalized_field.py b/bookmarks/migrations/0046_add_url_normalized_field.py
new file mode 100644
index 0000000..2b689ad
--- /dev/null
+++ b/bookmarks/migrations/0046_add_url_normalized_field.py
@@ -0,0 +1,18 @@
+# Generated by Django 5.2.3 on 2025-08-22 08:26
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookmarks", "0045_userprofile_hide_bundles_bookmarkbundle"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="bookmark",
+            name="url_normalized",
+            field=models.CharField(blank=True, db_index=True, max_length=2048),
+        ),
+    ]
diff --git a/bookmarks/migrations/0047_populate_url_normalized_field.py b/bookmarks/migrations/0047_populate_url_normalized_field.py
new file mode 100644
index 0000000..bb4fae2
--- /dev/null
+++ b/bookmarks/migrations/0047_populate_url_normalized_field.py
@@ -0,0 +1,38 @@
+# Generated by Django 5.2.3 on 2025-08-22 08:28
+
+from django.db import migrations, transaction
+from bookmarks.utils import normalize_url
+
+
+def populate_url_normalized(apps, schema_editor):
+    Bookmark = apps.get_model("bookmarks", "Bookmark")
+
+    batch_size = 500
+    with transaction.atomic():
+        qs = Bookmark.objects.all()
+        for start in range(0, qs.count(), batch_size):
+            batch = list(qs[start : start + batch_size])
+            for bookmark in batch:
+                bookmark.url_normalized = normalize_url(bookmark.url)
+            Bookmark.objects.bulk_update(
+                batch, ["url_normalized"], batch_size=batch_size
+            )
+
+
+def reverse_populate_url_normalized(apps, schema_editor):
+    Bookmark = apps.get_model("bookmarks", "Bookmark")
+    Bookmark.objects.all().update(url_normalized="")
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("bookmarks", "0046_add_url_normalized_field"),
+    ]
+
+    operations = [
+        migrations.RunPython(
+            populate_url_normalized,
+            reverse_populate_url_normalized,
+        ),
+    ]
diff --git a/bookmarks/models.py b/bookmarks/models.py
index fe7efce..2e860d7 100644
--- a/bookmarks/models.py
+++ b/bookmarks/models.py
@@ -14,7 +14,7 @@ from django.db.models.signals import post_save, post_delete
 from django.dispatch import receiver
 from django.http import QueryDict
 
-from bookmarks.utils import unique
+from bookmarks.utils import unique, normalize_url
 from bookmarks.validators import BookmarkURLValidator
 
 logger = logging.getLogger(__name__)
@@ -54,6 +54,7 @@ def build_tag_string(tag_names: List[str], delimiter: str = ","):
 
 class Bookmark(models.Model):
     url = models.CharField(max_length=2048, validators=[BookmarkURLValidator()])
+    url_normalized = models.CharField(max_length=2048, blank=True, db_index=True)
     title = models.CharField(max_length=512, blank=True)
     description = models.TextField(blank=True)
     notes = models.TextField(blank=True)
@@ -96,6 +97,10 @@ class Bookmark(models.Model):
         names = [tag.name for tag in self.tags.all()]
         return sorted(names)
 
+    def save(self, *args, **kwargs):
+        self.url_normalized = normalize_url(self.url)
+        super().save(*args, **kwargs)
+
     def __str__(self):
         return self.resolved_title + " (" + self.url[:30] + "...)"
 
diff --git a/bookmarks/services/bookmarks.py b/bookmarks/services/bookmarks.py
index 82b1fb2..923ba87 100644
--- a/bookmarks/services/bookmarks.py
+++ b/bookmarks/services/bookmarks.py
@@ -4,6 +4,7 @@ from typing import Union
 from django.utils import timezone
 
 from bookmarks.models import Bookmark, User, parse_tag_string
+from bookmarks.utils import normalize_url
 from bookmarks.services import auto_tagging
 from bookmarks.services import tasks
 from bookmarks.services import website_loader
@@ -19,8 +20,9 @@ def create_bookmark(
     disable_html_snapshot: bool = False,
 ):
     # If URL is already bookmarked, then update it
+    normalized_url = normalize_url(bookmark.url)
     existing_bookmark: Bookmark = Bookmark.objects.filter(
-        owner=current_user, url=bookmark.url
+        owner=current_user, url_normalized=normalized_url
     ).first()
 
     if existing_bookmark is not None:
diff --git a/bookmarks/tests/test_bookmark_edit_view.py b/bookmarks/tests/test_bookmark_edit_view.py
index bec1ee4..da7dc67 100644
--- a/bookmarks/tests/test_bookmark_edit_view.py
+++ b/bookmarks/tests/test_bookmark_edit_view.py
@@ -188,6 +188,25 @@ class BookmarkEditViewTestCase(TestCase, BookmarkFactoryMixin):
         edited_bookmark.refresh_from_db()
         self.assertNotEqual(edited_bookmark.url, existing_bookmark.url)
 
+    def test_should_prevent_duplicate_normalized_urls(self):
+        self.setup_bookmark(url="https://EXAMPLE.COM/path/?z=1&a=2")
+
+        edited_bookmark = self.setup_bookmark(url="http://different.com")
+
+        form_data = self.create_form_data({"url": "https://example.com/path?a=2&z=1"})
+        response = self.client.post(
+            reverse("linkding:bookmarks.edit", args=[edited_bookmark.id]), form_data
+        )
+
+        self.assertEqual(response.status_code, 422)
+        self.assertInHTML(
+            "<li>A bookmark with this URL already exists.</li>",
+            response.content.decode(),
+        )
+
+        edited_bookmark.refresh_from_db()
+        self.assertEqual(edited_bookmark.url, "http://different.com")
+
     def test_should_redirect_to_return_url(self):
         bookmark = self.setup_bookmark()
         form_data = self.create_form_data()
diff --git a/bookmarks/tests/test_bookmarks_api.py b/bookmarks/tests/test_bookmarks_api.py
index 5f22d03..ea77a0c 100644
--- a/bookmarks/tests/test_bookmarks_api.py
+++ b/bookmarks/tests/test_bookmarks_api.py
@@ -1047,6 +1047,29 @@ class BookmarksApiTestCase(LinkdingApiTestCase, BookmarkFactoryMixin):
             self.assertEqual(expected_metadata.description, metadata["description"])
             self.assertEqual(expected_metadata.preview_image, metadata["preview_image"])
 
+    def test_check_returns_bookmark_using_normalized_url(self):
+        self.authenticate()
+
+        # Create bookmark with one URL variant
+        bookmark = self.setup_bookmark(
+            url="https://EXAMPLE.COM/path/?z=1&a=2",
+            title="Example title",
+            description="Example description",
+        )
+
+        # Check with different URL variant that should normalize to the same URL
+        url = reverse("linkding:bookmark-check")
+        check_url = urllib.parse.quote_plus("https://example.com/path?a=2&z=1")
+        response = self.get(
+            f"{url}?url={check_url}", expected_status_code=status.HTTP_200_OK
+        )
+        bookmark_data = response.data["bookmark"]
+
+        # Should find the existing bookmark despite URL differences
+        self.assertIsNotNone(bookmark_data)
+        self.assertEqual(bookmark.id, bookmark_data["id"])
+        self.assertEqual(bookmark.title, bookmark_data["title"])
+
     def test_check_returns_no_auto_tags_if_none_configured(self):
         self.authenticate()
 
diff --git a/bookmarks/tests/test_bookmarks_service.py b/bookmarks/tests/test_bookmarks_service.py
index 42cb78d..a930580 100644
--- a/bookmarks/tests/test_bookmarks_service.py
+++ b/bookmarks/tests/test_bookmarks_service.py
@@ -95,6 +95,41 @@ class BookmarkServiceTestCase(TestCase, BookmarkFactoryMixin):
         # Saving a duplicate bookmark should not modify archive flag - right?
         self.assertFalse(updated_bookmark.is_archived)
 
+    def test_create_should_update_existing_bookmark_with_normalized_url(
+        self,
+    ):
+        original_bookmark = self.setup_bookmark(
+            url="https://EXAMPLE.com/path/?a=1&z=2", unread=False, shared=False
+        )
+        bookmark_data = Bookmark(
+            url="HTTPS://example.com/path?z=2&a=1",
+            title="Updated Title",
+            description="Updated description",
+        )
+        updated_bookmark = create_bookmark(
+            bookmark_data, "", self.get_or_create_test_user()
+        )
+
+        self.assertEqual(Bookmark.objects.count(), 1)
+        self.assertEqual(updated_bookmark.id, original_bookmark.id)
+        self.assertEqual(updated_bookmark.title, bookmark_data.title)
+
+    def test_create_should_populate_url_normalized_field(self):
+        bookmark_data = Bookmark(
+            url="https://EXAMPLE.COM/path/?z=1&a=2",
+            title="Test Title",
+            description="Test description",
+        )
+        created_bookmark = create_bookmark(
+            bookmark_data, "", self.get_or_create_test_user()
+        )
+
+        created_bookmark.refresh_from_db()
+        self.assertEqual(created_bookmark.url, "https://EXAMPLE.COM/path/?z=1&a=2")
+        self.assertEqual(
+            created_bookmark.url_normalized, "https://example.com/path?a=2&z=1"
+        )
+
     def test_create_should_create_web_archive_snapshot(self):
         with patch.object(
             tasks, "create_web_archive_snapshot"
diff --git a/bookmarks/tests/test_utils.py b/bookmarks/tests/test_utils.py
index 136cf70..7bdeb38 100644
--- a/bookmarks/tests/test_utils.py
+++ b/bookmarks/tests/test_utils.py
@@ -8,6 +8,7 @@ from bookmarks.utils import (
     humanize_absolute_date,
     humanize_relative_date,
     parse_timestamp,
+    normalize_url,
 )
 
 
@@ -182,3 +183,181 @@ class UtilsTestCase(TestCase):
 
         with self.assertRaises(ValueError):
             self.verify_timestamp(now, 1000000000)
+
+    def test_normalize_url_trailing_slash_handling(self):
+        test_cases = [
+            ("https://example.com/", "https://example.com"),
+            (
+                "https://example.com/path/",
+                "https://example.com/path",
+            ),
+            ("https://example.com/path/to/page/", "https://example.com/path/to/page"),
+            (
+                "https://example.com/path",
+                "https://example.com/path",
+            ),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_query_parameters(self):
+        test_cases = [
+            ("https://example.com?z=1&a=2", "https://example.com?a=2&z=1"),
+            ("https://example.com?c=3&b=2&a=1", "https://example.com?a=1&b=2&c=3"),
+            ("https://example.com?param=value", "https://example.com?param=value"),
+            ("https://example.com?", "https://example.com"),
+            (
+                "https://example.com?empty=&filled=value",
+                "https://example.com?empty=&filled=value",
+            ),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_case_sensitivity(self):
+        test_cases = [
+            (
+                "https://EXAMPLE.com/Path/To/Page",
+                "https://example.com/Path/To/Page",
+            ),
+            ("https://EXAMPLE.COM/API/v1/Users", "https://example.com/API/v1/Users"),
+            (
+                "HTTPS://EXAMPLE.COM/path",
+                "https://example.com/path",
+            ),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_special_characters_and_encoding(self):
+        test_cases = [
+            (
+                "https://example.com/path%20with%20spaces",
+                "https://example.com/path%20with%20spaces",
+            ),
+            ("https://example.com/caf%C3%A9", "https://example.com/caf%C3%A9"),
+            (
+                "https://example.com/path?q=hello%20world",
+                "https://example.com/path?q=hello%20world",
+            ),
+            ("https://example.com/pàth", "https://example.com/pàth"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_various_protocols(self):
+        test_cases = [
+            ("FTP://example.com", "ftp://example.com"),
+            ("HTTP://EXAMPLE.COM", "http://example.com"),
+            ("https://example.com", "https://example.com"),
+            ("file:///path/to/file", "file:///path/to/file"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_port_handling(self):
+        test_cases = [
+            ("https://example.com:8080", "https://example.com:8080"),
+            ("https://EXAMPLE.COM:8080", "https://example.com:8080"),
+            ("http://example.com:80", "http://example.com:80"),
+            ("https://example.com:443", "https://example.com:443"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_authentication_handling(self):
+        test_cases = [
+            ("https://user:pass@EXAMPLE.COM", "https://user:pass@example.com"),
+            ("https://user@EXAMPLE.COM", "https://user@example.com"),
+            ("ftp://admin:secret@EXAMPLE.COM", "ftp://admin:secret@example.com"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_fragment_handling(self):
+        test_cases = [
+            ("https://example.com#", "https://example.com"),
+            ("https://example.com#section", "https://example.com#section"),
+            ("https://EXAMPLE.COM/path#Section", "https://example.com/path#Section"),
+            ("https://EXAMPLE.COM/path/#Section", "https://example.com/path#Section"),
+            ("https://example.com?a=1#fragment", "https://example.com?a=1#fragment"),
+            (
+                "https://example.com?z=2&a=1#fragment",
+                "https://example.com?a=1&z=2#fragment",
+            ),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_edge_cases(self):
+        test_cases = [
+            ("", ""),
+            ("   ", ""),
+            ("   https://example.com   ", "https://example.com"),
+            ("not-a-url", "not-a-url"),
+            ("://invalid", "://invalid"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
+
+    def test_normalize_url_internationalized_domain_names(self):
+        test_cases = [
+            (
+                "https://xn--fsq.xn--0zwm56d",
+                "https://xn--fsq.xn--0zwm56d",
+            ),
+            ("https://测试.中国", "https://测试.中国"),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected.lower() if expected else expected, result)
+
+    def test_normalize_url_complex_query_parameters(self):
+        test_cases = [
+            (
+                "https://example.com?z=1&a=2&z=3&b=4",
+                "https://example.com?a=2&b=4&z=1&z=3",  # Multiple values for same key
+            ),
+            (
+                "https://example.com?param=value1&param=value2",
+                "https://example.com?param=value1&param=value2",
+            ),
+            (
+                "https://example.com?special=%21%40%23%24%25",
+                "https://example.com?special=%21%40%23%24%25",
+            ),
+        ]
+
+        for original, expected in test_cases:
+            with self.subTest(url=original):
+                result = normalize_url(original)
+                self.assertEqual(expected, result)
diff --git a/bookmarks/utils.py b/bookmarks/utils.py
index 27db7d4..da814fa 100644
--- a/bookmarks/utils.py
+++ b/bookmarks/utils.py
@@ -139,3 +139,49 @@ def generate_username(email, claims):
     else:
         username = email
     return unicodedata.normalize("NFKC", username)[:150]
+
+
+def normalize_url(url: str) -> str:
+    if not url or not isinstance(url, str):
+        return ""
+
+    url = url.strip()
+    if not url:
+        return ""
+
+    try:
+        parsed = urllib.parse.urlparse(url)
+
+        # Normalize the scheme to lowercase
+        scheme = parsed.scheme.lower()
+
+        # Normalize the netloc (domain) to lowercase
+        netloc = parsed.hostname.lower() if parsed.hostname else ""
+        if parsed.port:
+            netloc += f":{parsed.port}"
+        if parsed.username:
+            auth = parsed.username
+            if parsed.password:
+                auth += f":{parsed.password}"
+            netloc = f"{auth}@{netloc}"
+
+        # Remove trailing slashes from all paths
+        path = parsed.path.rstrip("/") if parsed.path else ""
+
+        # Sort query parameters alphabetically
+        query = ""
+        if parsed.query:
+            query_params = urllib.parse.parse_qsl(parsed.query, keep_blank_values=True)
+            query_params.sort(key=lambda x: (x[0], x[1]))
+            query = urllib.parse.urlencode(query_params, quote_via=urllib.parse.quote)
+
+        # Keep fragment as-is
+        fragment = parsed.fragment
+
+        # Reconstruct the normalized URL
+        return urllib.parse.urlunparse(
+            (scheme, netloc, path, parsed.params, query, fragment)
+        )
+
+    except (ValueError, AttributeError):
+        return url