diff --git a/backend/src/modules/user/schemas.py b/backend/src/modules/user/schemas.py
index 2565984b..b8e64fe9 100644
--- a/backend/src/modules/user/schemas.py
+++ b/backend/src/modules/user/schemas.py
@@ -1,7 +1,8 @@
+import re
 from datetime import datetime
 from typing import Annotated
 
-from pydantic import BaseModel, ConfigDict, EmailStr, Field
+from pydantic import BaseModel, ConfigDict, EmailStr, Field, field_validator
 
 from ..common.schemas import PersistentDeletion, TimestampSchema
 from .constants import NAME_MAX_LENGTH, USERNAME_MAX_LENGTH, USERNAME_PATTERN
@@ -68,7 +69,6 @@ class UserCreate(UserBase):
                 "uppercase letter, lowercase letter, and special character"
             ),
             examples=["Str1ngst!"],
-            pattern=r"^.{8,}|[0-9]+|[A-Z]+|[a-z]+|[^a-zA-Z0-9]+$",
         ),
     ]
     google_id: str | None = None
@@ -78,6 +78,23 @@ class UserCreate(UserBase):
     oauth_created_at: datetime | None = None
     oauth_updated_at: datetime | None = None
 
+    @field_validator("password")
+    def validate_password_strength(cls, v: str) -> str:
+        """Validate the password includes every character class in the description."""
+        if not re.search(r"[a-z]", v):
+            raise ValueError("Password must include at least one lowercase letter")
+
+        if not re.search(r"[A-Z]", v):
+            raise ValueError("Password must include at least one uppercase letter")
+
+        if not re.search(r"[0-9]", v):
+            raise ValueError("Password must include at least one number")
+
+        if not re.search(r"[^a-zA-Z0-9]", v):
+            raise ValueError("Password must include at least one special character")
+
+        return v
+
     model_config = ConfigDict(extra="forbid")
 
 
diff --git a/backend/tests/unit/modules/user/test_schemas.py b/backend/tests/unit/modules/user/test_schemas.py
new file mode 100644
index 00000000..09d93df2
--- /dev/null
+++ b/backend/tests/unit/modules/user/test_schemas.py
@@ -0,0 +1,47 @@
+"""Unit tests for the User schemas."""
+
+import pytest
+from pydantic import ValidationError
+
+from src.modules.user.schemas import UserCreate
+
+
+def _user_data(password: str) -> dict[str, str]:
+    return {
+        "name": "Test User",
+        "username": "testuser",
+        "email": "user.userson@example.com",
+        "password": password,
+    }
+
+
+def test_password_with_every_character_class_is_accepted():
+    """The documented example must keep working."""
+    user = UserCreate(**_user_data("Str1ngst!"))
+
+    assert user.password == "Str1ngst!"
+
+
+@pytest.mark.parametrize(
+    ("password", "missing"),
+    [
+        ("str1ngst!", "uppercase letter"),
+        ("STR1NGST!", "lowercase letter"),
+        ("Stringst!", "number"),
+        ("Str1ngst", "special character"),
+        ("abcdefgh", "uppercase letter"),
+        ("aaaaaaaaaaaa", "uppercase letter"),
+        ("        ", "lowercase letter"),
+    ],
+)
+def test_password_missing_a_character_class_is_rejected(password: str, missing: str):
+    """A password is rejected when any class from the description is missing."""
+    with pytest.raises(ValidationError, match=missing):
+        UserCreate(**_user_data(password))
+
+
+@pytest.mark.parametrize("password", ["Str1ng!", "Ab1!cde"])
+def test_password_shorter_than_eight_characters_is_rejected(password: str):
+    """Length stays enforced separately from the character classes."""
+    with pytest.raises(ValidationError, match="at least 8 characters"):
+        UserCreate(**_user_data(password))