diff --git a/features/consolidated_tool.feature b/features/consolidated_tool.feature
index 7a83a31f2..356850273 100644
--- a/features/consolidated_tool.feature
+++ b/features/consolidated_tool.feature
@@ -584,7 +584,7 @@ Feature: Consolidated Tool
   Scenario: attach_validation raises NotFoundError when validation does not exist
     Given a mock-based tool registry service
     Given the mock tool repo returns None for get_by_name
-    When I attempt to attach validation with mode "required" via the coverage service
+    When I attempt to attach validation via the coverage service
     Then a coverage NotFoundError should be raised with message containing "not found"
 
     # --- attach_validation: successful delegation ------------------------------
@@ -593,7 +593,7 @@ Feature: Consolidated Tool
   Scenario: attach_validation delegates to attachment repo when validation exists
     Given a mock-based tool registry service
     Given the mock tool repo returns a sentinel for get_by_name
-    When I attempt to attach validation with mode "required" via the coverage service
+    When I attempt to attach validation via the coverage service
     Then no error should be raised by the coverage service
 
 
@@ -661,15 +661,6 @@ Feature: Consolidated Tool
     Then the list result should be returned from list_all
     And no error should be raised by the fallback service
 
-    # --- attach_validation with invalid mode --------------------------------
-
-
-  Scenario: attach_validation raises ValidationError for invalid mode
-    Given a tool registry service with a standard mock repo
-    When I attach validation with invalid mode "bogus" via the fallback service
-    Then a fallback ValidationError should be raised with message containing "Invalid mode"
-
-
   # ============================================================
   # Originally from: tool_registry_service_uncovered_branches.feature
   # Feature: Tool Registry Service – uncovered branch paths
@@ -746,23 +737,6 @@ Feature: Consolidated Tool
     When I trs branch list tools with namespace "local" type "tool" source "builtin"
     Then the trs branch list result should come from the repo
 
-    # --- attach_validation: invalid mode (L168-169) ----------------------------
-
-
-  Scenario: attach_validation raises ValidationError for invalid mode
-    Given a trs branch mock-based tool registry service
-    Given a trs branch standard tool repo
-    When I trs branch attach validation with mode "strict"
-    Then a trs branch ValidationError should be raised with message containing "Invalid mode"
-
-
-  Scenario: attach_validation raises ValidationError for empty mode
-    Given a trs branch mock-based tool registry service
-    Given a trs branch standard tool repo
-    When I trs branch attach validation with mode "optional"
-    Then a trs branch ValidationError should be raised with message containing "Invalid mode"
-
-
   # ============================================================
   # Originally from: tool_runtime.feature
   # Feature: Tool Runtime Core
diff --git a/features/steps/tool_cli_steps.py b/features/steps/tool_cli_steps.py
index 7e85f159b..a12335429 100644
--- a/features/steps/tool_cli_steps.py
+++ b/features/steps/tool_cli_steps.py
@@ -522,18 +522,6 @@ def step_run_validation_attach_project(
         )
 
 
-@when(
-    'I run validation CLI attach with mode "{resource}" "{val_name}" mode is "{mode}"'
-)
-def step_run_validation_attach_mode(
-    context: Context, resource: str, val_name: str, mode: str
-) -> None:
-    with _patch_val_svc(context):
-        context.validation_result = _runner.invoke(
-            validation_app, ["attach", resource, val_name, "--mode", mode]
-        )
-
-
 @when(
     'I run validation CLI attach with extra args "{resource}" "{val_name}" '
     'arg is "{arg}"'
diff --git a/features/steps/tool_registry_service_coverage_steps.py b/features/steps/tool_registry_service_coverage_steps.py
index f2d5d522e..70c64e7dc 100644
--- a/features/steps/tool_registry_service_coverage_steps.py
+++ b/features/steps/tool_registry_service_coverage_steps.py
@@ -144,7 +144,10 @@ def step_repo_returns_none(context: Context) -> None:
 
 @given("the mock tool repo returns a sentinel for get_by_name")
 def step_repo_returns_sentinel(context: Context) -> None:
-    context.cov_tool_repo._get_by_name_return = {"name": "local/some-check"}
+    context.cov_tool_repo._get_by_name_return = {
+        "name": "local/some-check",
+        "mode": "required",
+    }
 
 
 # ---------------------------------------------------------------------------
@@ -181,13 +184,12 @@ def step_when_remove(context: Context, name: str) -> None:
         context.cov_error = exc
 
 
-@when('I attempt to attach validation with mode "{mode}" via the coverage service')
-def step_when_attach(context: Context, mode: str) -> None:
+@when("I attempt to attach validation via the coverage service")
+def step_when_attach(context: Context) -> None:
     try:
         context.cov_result = context.cov_service.attach_validation(
             resource_id="res-001",
             validation_name="local/some-check",
-            mode=mode,
         )
         context.cov_error = None
     except Exception as exc:
diff --git a/features/steps/tool_registry_service_fallback_coverage_steps.py b/features/steps/tool_registry_service_fallback_coverage_steps.py
index f642d7858..0049c2142 100644
--- a/features/steps/tool_registry_service_fallback_coverage_steps.py
+++ b/features/steps/tool_registry_service_fallback_coverage_steps.py
@@ -327,7 +327,6 @@ def step_when_attach_invalid_mode(context: Context, mode: str) -> None:
         context.fb_result = context.fb_service.attach_validation(
             validation_name="local/check",
             resource_id="res-001",
-            mode=mode,
         )
         context.fb_error = None
     except Exception as exc:
diff --git a/features/steps/tool_registry_service_uncovered_branches_steps.py b/features/steps/tool_registry_service_uncovered_branches_steps.py
index 2f92a783f..974013b29 100644
--- a/features/steps/tool_registry_service_uncovered_branches_steps.py
+++ b/features/steps/tool_registry_service_uncovered_branches_steps.py
@@ -405,7 +405,6 @@ def step_trs_branch_attach_invalid_mode(context: Context, mode: str) -> None:
         context.trs_b_result = context.trs_b_service.attach_validation(
             validation_name="local/some-validation",
             resource_id="res-001",
-            mode=mode,
         )
         context.trs_b_error = None
     except Exception as exc:
diff --git a/features/steps/tool_registry_steps.py b/features/steps/tool_registry_steps.py
index 0c19ee8ad..e6dbcd724 100644
--- a/features/steps/tool_registry_steps.py
+++ b/features/steps/tool_registry_steps.py
@@ -402,7 +402,6 @@ def step_service_attach(context: Context, val_name: str, res_id: str) -> None:
     context.service_attachment = context.tool_service.attach_validation(
         validation_name=val_name,
         resource_id=res_id,
-        mode="required",
     )
     context.tool_session.commit()
 
@@ -419,7 +418,6 @@ def step_service_given_attached(context: Context, val_name: str, res_id: str) ->
     context.service_attachment = context.tool_service.attach_validation(
         validation_name=val_name,
         resource_id=res_id,
-        mode="required",
     )
     context.tool_session.commit()
 
diff --git a/features/tool_cli.feature b/features/tool_cli.feature
index b1f9b0652..a69840940 100644
--- a/features/tool_cli.feature
+++ b/features/tool_cli.feature
@@ -202,11 +202,6 @@ Feature: Tool and Validation CLI commands
     When I run validation CLI attach scoped "resource/r1" "local/test-val" with project "myproj"
     Then the validation CLI attach should succeed
 
-  Scenario: Attach validation with mode informational
-    Given a mocked validation exists for attaching
-    When I run validation CLI attach with mode "resource/r1" "local/test-val" mode is "informational"
-    Then the validation CLI attach should succeed
-
   Scenario: Attach validation with extra args
     Given a mocked validation exists for attaching
     When I run validation CLI attach with extra args "resource/r1" "local/test-val" arg is "threshold=80"
diff --git a/robot/helper_wf04_multi_project_dependency.py b/robot/helper_wf04_multi_project_dependency.py
index f66e05f50..895a39c01 100644
--- a/robot/helper_wf04_multi_project_dependency.py
+++ b/robot/helper_wf04_multi_project_dependency.py
@@ -289,7 +289,6 @@ def cmd_register_projects() -> None:
         tool_svc.attach_validation(
             validation_name=_VALIDATION_NAME,
             resource_id=info["resource"],
-            mode="required",
             project_name=proj_name,
         )
     # Verify attachments
@@ -637,7 +636,6 @@ def cmd_full_lifecycle() -> None:
         tool_svc.attach_validation(
             validation_name=_VALIDATION_NAME,
             resource_id=info["resource"],
-            mode="required",
             project_name=proj_name,
         )
 
diff --git a/robot/helper_wf07_cicd.py b/robot/helper_wf07_cicd.py
index 5d0d19669..18a08b876 100644
--- a/robot/helper_wf07_cicd.py
+++ b/robot/helper_wf07_cicd.py
@@ -244,7 +244,6 @@ def validation_attach() -> None:
             attachment = svc.attach_validation(
                 validation_name=vname,
                 resource_id=resource_id,
-                mode="required",
                 project_name="local/ci-workspace",
             )
             assert attachment is not None, f"Attachment for {vname} must be created"
diff --git a/robot/wf02_test_generation_validation.py b/robot/wf02_test_generation_validation.py
index 93ad4dc8f..f0247daa7 100644
--- a/robot/wf02_test_generation_validation.py
+++ b/robot/wf02_test_generation_validation.py
@@ -282,7 +282,6 @@ def _register_attach_and_run_validation(
     tool_service.attach_validation(
         validation_name="local/auth-coverage",
         resource_id=resource_id,
-        mode="required",
         plan_id=plan_id,
         args={"target": target},
     )
diff --git a/src/cleveragents/application/services/tool_registry_service.py b/src/cleveragents/application/services/tool_registry_service.py
index a87355980..c52fa95ac 100644
--- a/src/cleveragents/application/services/tool_registry_service.py
+++ b/src/cleveragents/application/services/tool_registry_service.py
@@ -9,7 +9,7 @@ from __future__ import annotations
 
 from typing import Any
 
-from cleveragents.core.exceptions import NotFoundError, ValidationError
+from cleveragents.core.exceptions import NotFoundError
 from cleveragents.domain.models.core.tool import Tool
 from cleveragents.infrastructure.database.repositories import (
     ToolRegistryRepository,
@@ -143,17 +143,19 @@ class ToolRegistryService:
         self,
         validation_name: str,
         resource_id: str,
-        mode: str = "required",
         project_name: str | None = None,
         plan_id: str | None = None,
         args: dict[str, Any] | None = None,
     ) -> Any:
         """Attach a validation to a resource.
 
+        The validation mode (``required`` or ``informational``) is read from
+        the validation's registered definition — it is not an attach-time
+        override.
+
         Args:
             validation_name: Name of the validation tool to attach.
             resource_id: Resource reference string.
-            mode: ``required`` or ``informational``.
             project_name: Optional project scope.
             plan_id: Optional plan scope.
             args: Optional invocation arguments.
@@ -165,9 +167,6 @@ class ToolRegistryService:
             NotFoundError: If the validation tool does not exist.
             DatabaseError: On persistence failure.
         """
-        if mode not in {"required", "informational"}:
-            raise ValidationError(f"Invalid mode '{mode}'")
-
         # Verify validation exists
         existing = self._tool_repo.get_by_name(validation_name)
         if existing is None:
@@ -176,10 +175,17 @@ class ToolRegistryService:
                 resource_id=validation_name,
             )
 
+        # Read mode from the validation's registered definition
+        if isinstance(existing, dict):
+            mode = existing.get("mode", "required")
+        else:
+            mode = getattr(existing, "mode", "required")
+        mode_str: str = str(mode) if mode is not None else "required"
+
         return self._attachment_repo.attach(
             validation_name=validation_name,
             resource_id=resource_id,
-            mode=mode,
+            mode=mode_str,
             project_name=project_name,
             plan_id=plan_id,
             args=args,
diff --git a/src/cleveragents/cli/commands/validation.py b/src/cleveragents/cli/commands/validation.py
index d931b97b3..82c951288 100644
--- a/src/cleveragents/cli/commands/validation.py
+++ b/src/cleveragents/cli/commands/validation.py
@@ -265,10 +265,6 @@ def attach(
         str | None,
         typer.Option("--plan", help="Plan ID scope"),
     ] = None,
-    mode: Annotated[
-        str,
-        typer.Option("--mode", "-m", help="Validation mode: required or informational"),
-    ] = "required",
     fmt: Annotated[
         str,
         typer.Option("--format", "-f", help=_FORMAT_HELP),
@@ -276,10 +272,12 @@ def attach(
 ) -> None:
     """Attach a validation to a resource.
 
+    The validation mode (required or informational) is determined by the
+    validation's registered definition, not overridden at attach time.
+
     Examples:
         agents validation attach git-checkout/my-repo local/coverage-check
         agents validation attach --project myproj git-checkout/my-repo local/lint
-        agents validation attach --mode informational res1 local/val1
     """
     try:
         # Parse extra args
@@ -300,7 +298,6 @@ def attach(
         attachment = service.attach_validation(
             validation_name=validation_name,
             resource_id=resource,
-            mode=mode,
             project_name=project,
             plan_id=plan_id,
             args=extra_args,
diff --git a/src/cleveragents/infrastructure/database/repositories.py b/src/cleveragents/infrastructure/database/repositories.py
index b193719b4..2866b3a28 100644
--- a/src/cleveragents/infrastructure/database/repositories.py
+++ b/src/cleveragents/infrastructure/database/repositories.py
@@ -3733,6 +3733,7 @@ class ToolRepository(ToolRegistryRepository):
             output_schema=row.output_schema,
             tool_type=cast(str, row.tool_type),
             source=cast(str, row.source),
+            mode=cast(str, row.mode) if row.mode is not None else None,
         )