diff --git a/packages/notte-browser/src/notte_browser/session.py b/packages/notte-browser/src/notte_browser/session.py
index 4b77232ac..525a730f0 100644
--- a/packages/notte-browser/src/notte_browser/session.py
+++ b/packages/notte-browser/src/notte_browser/session.py
@@ -65,6 +65,7 @@
 from notte_core.data.space import DataSpace, ImageData, StructuredData, TBaseModel
 from notte_core.errors.actions import InvalidActionError
 from notte_core.errors.base import NotteBaseError
+from notte_core.errors.processing import CredentialFieldValidationError
 from notte_core.errors.provider import RateLimitError
 from notte_core.profiling import profiler
 from notte_core.space import ActionSpace
@@ -545,6 +546,10 @@ async def _action_with_vault(self, action: BaseAction) -> BaseAction:
                     outerHTML=await locator.evaluate("el => el.outerHTML"),
                 )
             return await self.vault.replace_credentials(action, attrs, snapshot)
+        except CredentialFieldValidationError:
+            # Sentinel placeholder used on an invalid target element — surface loudly instead of
+            # silently typing the literal placeholder string into the field.
+            raise
         except ValueError as e:
             # Credential field not found in vault (e.g., vault has email but action needs username)
             # Return original action - it will fail at execution with a clearer error
diff --git a/packages/notte-core/src/notte_core/credentials/base.py b/packages/notte-core/src/notte_core/credentials/base.py
index 01dc6745b..66e687968 100644
--- a/packages/notte-core/src/notte_core/credentials/base.py
+++ b/packages/notte-core/src/notte_core/credentials/base.py
@@ -26,7 +26,7 @@
 from notte_core.common.types import TResponseFormat
 from notte_core.credentials.types import ValueWithPlaceholder, get_str_value
 from notte_core.errors.actions import NoCredentialsFoundError
-from notte_core.errors.processing import InvalidPlaceholderError
+from notte_core.errors.processing import CredentialFieldValidationError, InvalidPlaceholderError
 from notte_core.profiling import profiler
 from notte_core.utils.url import get_root_domain
 
@@ -692,7 +692,12 @@ async def replace_credentials(
                     if cred_class is MFAField and isinstance(action, FillAction):
                         action = MultiFactorFillAction(id=action.id, value=action.value)
                 else:
-                    logger.trace(f"Could not validate element with attrs {attrs} for {cred_key}")
+                    # The caller passed a known sentinel placeholder, so they clearly intended a
+                    # credential substitution — but the targeted element doesn't satisfy the field's
+                    # validation (e.g. a password placeholder pointed at a <label> instead of the
+                    # <input type="password">). Raising here prevents the literal sentinel string
+                    # from being silently typed into the field.
+                    raise CredentialFieldValidationError(placeholder_value, cred_key, attrs)
             else:
                 # dont validate because element chosen by regex
                 assert isinstance(action.value, dict)
diff --git a/packages/notte-core/src/notte_core/errors/processing.py b/packages/notte-core/src/notte_core/errors/processing.py
index cc91b703a..838f34815 100644
--- a/packages/notte-core/src/notte_core/errors/processing.py
+++ b/packages/notte-core/src/notte_core/errors/processing.py
@@ -98,6 +98,31 @@ def __init__(self, placeholder: str) -> None:
         )
 
 
+class CredentialFieldValidationError(NotteBaseError):
+    """Raised when a sentinel placeholder is used to fill an element that fails the credential
+    field's element-validation check (e.g. a password placeholder targeted at a non-password
+    element such as a <label>). Without this error the substitution would silently no-op and the
+    literal placeholder string would be typed into the field."""
+
+    def __init__(self, placeholder: str, cred_key: str, attrs: object) -> None:
+        dev_message = (
+            f"Sentinel placeholder {placeholder!r} for credential field {cred_key!r} was supplied, "
+            f"but the targeted element failed validate_element. Element attrs: {attrs!r}. "
+            f"Common cause: the action targeted a wrapper (e.g. <label>) instead of the actual "
+            f"<input>. Re-target the input element directly."
+        )
+        agent_message = (
+            f"Could not fill credential {cred_key!r}: targeted element is not a valid {cred_key!r} input. "
+            f"Re-locate the actual input field and retry."
+        )
+        user_message = "Credential placeholder used on an element that is not a valid target for that field."
+        super().__init__(
+            agent_message=agent_message,
+            user_message=user_message,
+            dev_message=dev_message,
+        )
+
+
 class ScrapeFailedError(NotteBaseError):
     def __init__(self, error_message: str) -> None:
         super().__init__(
diff --git a/tests/test_session_vault_helpers.py b/tests/test_session_vault_helpers.py
index 6aa171d58..fc1133178 100644
--- a/tests/test_session_vault_helpers.py
+++ b/tests/test_session_vault_helpers.py
@@ -1,9 +1,12 @@
 import asyncio
 
+import pytest
 from notte_browser.session import NotteSession
-from notte_core.actions import FormFillAction
+from notte_core.actions import FillAction, FormFillAction
 from notte_core.credentials import EMAIL, PASSWORD, USERNAME
+from notte_core.credentials.base import LocatorAttributes
 from notte_core.credentials.types import ValueWithPlaceholder
+from notte_core.errors.processing import CredentialFieldValidationError
 
 from tests.mock.mock_vault import MockVault
 from tests.mock.snapshot_factory import make_snapshot
@@ -112,3 +115,76 @@ def test_session_vault_action_without_placeholders_passes_through() -> None:
     result = asyncio.run(session._action_with_vault(action))
     # Should pass through unchanged since no placeholders
     assert result is action
+
+
+def test_password_placeholder_on_invalid_element_raises() -> None:
+    """A password sentinel typed into a non-password element (e.g. a <label>) must raise instead
+    of silently no-op'ing. Otherwise the literal placeholder string is typed into the field."""
+    vault = MockVault({"https://example.com": {"username": "real_user", "password": "s3cr3t"}})
+    snapshot = make_snapshot("https://example.com")
+
+    # Mimics the locator attrs you get when targeting a <label> instead of <input type="password">:
+    # the type attribute is None because <label> has no type.
+    label_attrs = LocatorAttributes(type=None, autocomplete=None, outerHTML="<label>Password</label>")
+    action = FillAction(id="M2", value=PASSWORD)
+
+    with pytest.raises(CredentialFieldValidationError) as exc_info:
+        asyncio.run(vault.replace_credentials(action, label_attrs, snapshot))
+
+    # Error message should name the credential and hint at the wrong-element cause
+    assert "password" in exc_info.value.dev_message
+    assert PASSWORD in exc_info.value.dev_message
+
+    # And the action value must not have been mutated to a ValueWithPlaceholder — caller decides
+    # whether to recover, but the literal placeholder must not silently leak into typing.
+    assert action.value == PASSWORD
+
+
+def test_password_placeholder_on_password_input_substitutes() -> None:
+    """Happy path: when the targeted element really is type=password, substitution proceeds."""
+    vault = MockVault({"https://example.com": {"username": "real_user", "password": "s3cr3t"}})
+    snapshot = make_snapshot("https://example.com")
+
+    input_attrs = LocatorAttributes(
+        type="password", autocomplete="current-password", outerHTML='<input type="password">'
+    )
+    action = FillAction(id="I2", value=PASSWORD)
+    updated = asyncio.run(vault.replace_credentials(action, input_attrs, snapshot))
+
+    assert isinstance(updated.value, ValueWithPlaceholder)
+    assert updated.value.get_secret_value() == "s3cr3t"
+
+
+def test_username_placeholder_unaffected_by_validation_change() -> None:
+    """UserNameField.validate_element returns True unconditionally, so username substitution
+    still works even when targeting a non-input wrapper. This pins the asymmetric design that
+    only PasswordField (and other typed fields) gates on element type."""
+    vault = MockVault({"https://example.com": {"username": "real_user", "password": "s3cr3t"}})
+    snapshot = make_snapshot("https://example.com")
+
+    label_attrs = LocatorAttributes(type=None, autocomplete=None, outerHTML="<label>Username</label>")
+    action = FillAction(id="M1", value=USERNAME)
+    updated = asyncio.run(vault.replace_credentials(action, label_attrs, snapshot))
+
+    assert isinstance(updated.value, ValueWithPlaceholder)
+    assert updated.value.get_secret_value() == "real_user"
+
+
+def test_session_action_with_vault_propagates_validation_error() -> None:
+    """The session-level catch must not swallow CredentialFieldValidationError — otherwise the
+    placeholder leaks into the typed value despite the new raise."""
+    vault = MockVault({"https://example.com": {"username": "u", "password": "p"}})
+    session = NotteSession(vault=vault)
+    session.snapshot = make_snapshot("https://example.com")
+
+    # Force the validation-failing path by stubbing locate() to return None: replace_credentials
+    # then runs against the default-empty LocatorAttributes (type=None), which fails the
+    # PasswordField check.
+    async def _no_locator(_action):
+        return None
+
+    session.locate = _no_locator  # type: ignore[method-assign]
+
+    action = FillAction(id="M2", value=PASSWORD)
+    with pytest.raises(CredentialFieldValidationError):
+        asyncio.run(session._action_with_vault(action))