diff --git a/CHANGELOG.md b/CHANGELOG.md
index a113d41..8af5986 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,18 @@ All notable changes to the AxonFlow Python SDK will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [5.1.0] - 2026-03-19
+
+### Added
+
+- New `langgraph` optional extra for MCP tool interception: `pip install 'axonflow[langgraph]'`. The `mcp` package is now an opt-in dependency rather than being imported unconditionally at the package level.
+
+### Fixed
+
+- `mcp_tool_interceptor()` now wraps redacted output in a `CallToolResult` instead of returning a plain `str`. Previously, when `mcp_check_output` applied redaction, the interceptor returned the redacted string directly, causing `AttributeError: 'str' object has no attribute 'content'` in `langchain-mcp-adapters`.
+
+---
+
 ## [5.0.0] - 2026-03-16
 
 ### Breaking Changes
diff --git a/axonflow/_version.py b/axonflow/_version.py
index e8038eb..91284fe 100644
--- a/axonflow/_version.py
+++ b/axonflow/_version.py
@@ -1,3 +1,3 @@
 """Single source of truth for the AxonFlow SDK version."""
 
-__version__ = "5.0.0"
+__version__ = "5.1.0"
diff --git a/axonflow/adapters/langgraph.py b/axonflow/adapters/langgraph.py
index 5d25822..06456bd 100644
--- a/axonflow/adapters/langgraph.py
+++ b/axonflow/adapters/langgraph.py
@@ -538,6 +538,15 @@ def mcp_tool_interceptor(
             An async callable ``(request, handler) -> result`` suitable for
             ``MultiServerMCPClient(tool_interceptors=[...])``.
         """
+        try:
+            from mcp.types import CallToolResult, TextContent  # noqa: PLC0415
+        except ImportError as exc:
+            msg = (
+                "The 'mcp' package is required to use mcp_tool_interceptor. "
+                "Install it with: pip install 'axonflow[langgraph]'"
+            )
+            raise ImportError(msg) from exc
+
         opts = options or MCPInterceptorOptions()
 
         def _default_connector_type(request: Any) -> str:
@@ -574,7 +583,9 @@ async def _interceptor(request: Any, handler: Callable[..., Any]) -> Any:
                     output_check.block_reason or "Tool result blocked by policy"
                 )
             if output_check.redacted_data is not None:
-                return output_check.redacted_data
+                return CallToolResult(
+                    content=[TextContent(type="text", text=output_check.redacted_data)]
+                )
 
             return result
 
diff --git a/pyproject.toml b/pyproject.toml
index b1a7969..943297f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "axonflow"
-version = "5.0.0"
+version = "5.1.0"
 description = "AxonFlow Python SDK - Enterprise AI Governance in 3 Lines of Code"
 readme = "README.md"
 license = {text = "MIT"}
@@ -52,6 +52,7 @@ dev = [
     "black>=23.0.0",
     "isort>=5.12.0",
     "pre-commit>=3.0.0",
+    "mcp>=1.0.0",
 ]
 docs = [
     "sphinx>=7.0.0",
@@ -61,9 +62,11 @@ docs = [
 ]
 openai = ["openai>=1.0.0"]
 anthropic = ["anthropic>=0.18.0"]
+langgraph = ["mcp>=1.0.0"]
 all = [
     "openai>=1.0.0",
     "anthropic>=0.18.0",
+    "mcp>=1.0.0",
 ]
 
 [project.urls]
diff --git a/tests/test_langgraph_adapter.py b/tests/test_langgraph_adapter.py
index efd0b59..69e54bf 100644
--- a/tests/test_langgraph_adapter.py
+++ b/tests/test_langgraph_adapter.py
@@ -7,6 +7,7 @@
 from unittest.mock import AsyncMock, MagicMock
 
 import pytest
+from mcp.types import CallToolResult, TextContent
 
 from axonflow import AxonFlow
 from axonflow.adapters.langgraph import AxonFlowLangGraphAdapter, MCPInterceptorOptions
@@ -192,7 +193,10 @@ async def test_returns_redacted_data_when_present(
 
         result = await adapter.mcp_tool_interceptor()(MagicMock(), handler)
 
-        assert result == "[REDACTED]"
+        assert isinstance(result, CallToolResult)
+        assert len(result.content) == 1
+        assert isinstance(result.content[0], TextContent)
+        assert result.content[0].text == "[REDACTED]"
 
     @pytest.mark.asyncio
     async def test_returns_original_result_when_no_redaction(