LangChain Integration

Overview

The Secure MCP Gateway provides two Python modules for protecting LangChain and LangGraph applications:

LangChain Module - BaseCallbackHandler for any LangChain component
LangGraph Module - pre_model_hook and post_model_hook for LangGraph agents

Use the EnkryptGuardrailsHandler to protect any LangChain component including LLMs, chains, agents, tools, and retrievers.

Installation

cd hooks/langchain
pip install -r requirements.txt

Configure Guardrails

cp guardrails_config_example.json guardrails_config.json
# Edit with your API key

export ENKRYPT_API_KEY="your-api-key"

Basic Usage

from langchain_openai import ChatOpenAI
from enkrypt_guardrails_handler import EnkryptGuardrailsHandler

# Create the guardrails handler
handler = EnkryptGuardrailsHandler()

# Use with any LangChain component
llm = ChatOpenAI(model="gpt-4", callbacks=[handler])

# The handler will automatically validate inputs and monitor outputs
response = llm.invoke("What is the weather today?")

Supported Hooks

The EnkryptGuardrailsHandler implements all LangChain BaseCallbackHandler methods:

Hook	Description	Default Checks
`on_llm_start`	Before LLM call	injection_attack, pii, toxicity
`on_llm_end`	After LLM response	pii, toxicity, nsfw
`on_chat_model_start`	Before chat model call	injection_attack, pii, toxicity
`on_chain_start`	Before chain execution	injection_attack, pii
`on_chain_end`	After chain completion	pii, toxicity
`on_tool_start`	Before tool execution	injection_attack, pii
`on_tool_end`	After tool execution	pii
`on_agent_action`	On agent decision	injection_attack
`on_agent_finish`	On agent completion	pii, toxicity, nsfw
`on_retriever_start`	Before retriever query	injection_attack
`on_retriever_end`	After document retrieval	pii

Usage Examples

With Chains

from langchain_core.prompts import ChatPromptTemplate
from langchain_openai import ChatOpenAI
from enkrypt_guardrails_handler import EnkryptGuardrailsHandler

handler = EnkryptGuardrailsHandler()

prompt = ChatPromptTemplate.from_messages([
    ("system", "You are a helpful assistant."),
    ("user", "{input}")
])

llm = ChatOpenAI()

# Add handler to the chain
chain = prompt | llm
chain = chain.with_config(callbacks=[handler])

response = chain.invoke({"input": "What is machine learning?"})

With Agents

from langchain_openai import ChatOpenAI
from langchain.agents import create_react_agent, AgentExecutor
from langchain_core.tools import tool
from enkrypt_guardrails_handler import EnkryptGuardrailsHandler

handler = EnkryptGuardrailsHandler()

@tool
def search(query: str) -> str:
    """Search for information."""
    return f"Results for: {query}"

llm = ChatOpenAI()
tools = [search]

# Create agent with guardrails
agent = create_react_agent(llm, tools, prompt)
agent_executor = AgentExecutor(
    agent=agent,
    tools=tools,
    callbacks=[handler]
)

result = agent_executor.invoke({"input": "Search for Python tutorials"})

With Retrievers (RAG)

from langchain_openai import OpenAIEmbeddings, ChatOpenAI
from langchain_community.vectorstores import FAISS
from langchain.chains import RetrievalQA
from enkrypt_guardrails_handler import EnkryptGuardrailsHandler

handler = EnkryptGuardrailsHandler()

# Create retriever
embeddings = OpenAIEmbeddings()
vectorstore = FAISS.from_texts(["Document 1", "Document 2"], embeddings)
retriever = vectorstore.as_retriever()

# Create RAG chain with guardrails
llm = ChatOpenAI()
qa_chain = RetrievalQA.from_chain_type(
    llm=llm,
    retriever=retriever,
    callbacks=[handler]
)

result = qa_chain.invoke("What is in Document 1?")

Audit-Only Mode

# Log violations without blocking
handler = EnkryptGuardrailsHandler(
    raise_on_violation=False,  # Don't raise exceptions
    audit_only=True,           # Just log violations
)

Disable Sensitive Tool Blocking

handler = EnkryptGuardrailsHandler(
    block_sensitive_tools=False,  # Allow sensitive tools
)

LangGraph Integration

For LangGraph’s create_react_agent, use pre_model_hook and post_model_hook.

Installation

cd hooks/langgraph
pip install -r requirements.txt

Basic Usage

from langchain_openai import ChatOpenAI
from langchain_core.tools import tool
from enkrypt_guardrails_hook import create_pre_model_hook, create_post_model_hook
from langgraph.prebuilt import create_react_agent

# Define your tools
@tool
def search(query: str) -> str:
    """Search for information."""
    return f"Results for {query}"

# Create model and tools
model = ChatOpenAI(model="gpt-4")
tools = [search]

# Create hooks
pre_hook = create_pre_model_hook(block_on_violation=True)
post_hook = create_post_model_hook(block_on_violation=True)

# Create agent with guardrails
agent = create_react_agent(
    model,
    tools,
    pre_model_hook=pre_hook,
    post_model_hook=post_hook,
)

# Use the agent
result = agent.invoke({"messages": [("user", "Search for LangGraph docs")]})

Convenience Functions

from enkrypt_guardrails_hook import create_protected_agent, create_audit_only_agent

# Create fully protected agent
agent = create_protected_agent(
    model,
    tools,
    block_on_violation=True,
    wrap_agent_tools=True,  # Also protect tool calls
)

# Create audit-only agent
audit_agent = create_audit_only_agent(model, tools)

Tool Wrapping

from enkrypt_guardrails_hook import wrap_tools, EnkryptToolWrapper

# Wrap multiple tools
protected_tools = wrap_tools(tools, block_on_violation=True)

# Or wrap individually
wrapper = EnkryptToolWrapper(
    my_tool,
    block_on_violation=True,
    check_inputs=True,
    check_outputs=True,
)
protected_tool = wrapper.tool

Configuration

LangChain Configuration

guardrails_config.json

{
  "enkrypt_api": {
    "url": "https://api.enkryptai.com/guardrails/policy/detect",
    "api_key": "YOUR_ENKRYPT_API_KEY",
    "ssl_verify": true,
    "timeout": 15,
    "fail_silently": true
  },
  "on_llm_start": {
    "enabled": true,
    "guardrail_name": "Sample Airline Guardrail",
    "block": ["injection_attack", "pii", "toxicity"]
  },
  "on_tool_start": {
    "enabled": true,
    "guardrail_name": "Tool Input Policy",
    "block": ["injection_attack", "pii"]
  },
  "sensitive_tools": [
    "execute_sql",
    "run_command",
    "shell_*",
    "bash",
    "delete_*",
    "write_file",
    "python_repl"
  ]
}

LangGraph Configuration

guardrails_config.json

{
  "enkrypt_api": {
    "url": "https://api.enkryptai.com/guardrails/policy/detect",
    "api_key": "YOUR_ENKRYPT_API_KEY",
    "ssl_verify": true,
    "timeout": 15,
    "fail_silently": true
  },
  "pre_model_hook": {
    "enabled": true,
    "guardrail_name": "Sample Airline Guardrail",
    "block": ["injection_attack", "pii", "toxicity", "nsfw"]
  },
  "post_model_hook": {
    "enabled": true,
    "guardrail_name": "Sample Airline Guardrail",
    "block": ["pii", "toxicity", "nsfw"]
  },
  "before_tool_call": {
    "enabled": true,
    "guardrail_name": "Sample Airline Guardrail",
    "block": ["injection_attack", "pii"]
  },
  "after_tool_call": {
    "enabled": true,
    "guardrail_name": "Sample Airline Guardrail",
    "block": ["pii"]
  }
}

Available Detectors

Detector	Description
`injection_attack`	Prompt injection attempts
`pii`	Personal Identifiable Information
`toxicity`	Toxic/harmful content
`nsfw`	Not Safe For Work content
`keyword_detector`	Banned keywords
`policy_violation`	Custom policy violations
`bias`	Biased content
`topic_detector`	Off-topic content

Logging

Logs are written to ~/langchain/guardrails_logs/ or ~/langgraph/guardrails_logs/:

on_llm_start.jsonl / pre_model_hook.jsonl - Input validation
on_llm_end.jsonl / post_model_hook.jsonl - Output validation
on_tool_start.jsonl / before_tool_call.jsonl - Tool input checks
combined_audit.jsonl - All events combined
security_alerts.jsonl - Security violations

View Logs

# View latest blocks
tail -5 ~/langchain/guardrails_logs/security_alerts.jsonl

# View tool executions
tail -10 ~/langchain/guardrails_logs/on_tool_start.jsonl

Metrics

from enkrypt_guardrails_handler import get_guardrails_metrics

# Get all metrics
metrics = get_guardrails_metrics()

# Get metrics for specific hook
llm_metrics = get_guardrails_metrics("on_llm_start")
print(f"Total calls: {llm_metrics['total_calls']}")
print(f"Blocked: {llm_metrics['blocked_calls']}")
print(f"Avg latency: {llm_metrics['avg_latency_ms']:.2f}ms")

Error Handling

from enkrypt_guardrails_handler import (
    EnkryptGuardrailsHandler,
    GuardrailsViolationError,
    SensitiveToolBlockedError,
)

handler = EnkryptGuardrailsHandler()

try:
    response = llm.invoke("malicious prompt")
except GuardrailsViolationError as e:
    print(f"Guardrails violation: {e}")
    print(f"Hook: {e.hook_name}")
    print(f"Violations: {e.violations}")
except SensitiveToolBlockedError as e:
    print(f"Sensitive tool blocked: {e.tool_name}")
    print(f"Reason: {e.reason}")

Comparison

Feature	LangChain Module	LangGraph Module
Hook Pattern	`BaseCallbackHandler`	`pre_model_hook` / `post_model_hook`
Scope	Any LangChain component	LangGraph agents only
Tool Hooks	`on_tool_start/end`	Tool wrappers
Chain Support	Yes	No (use state hooks)
Retriever Support	Yes	No
Agent Support	Yes	Yes

Use LangChain module for:

Standalone LangChain components
Chains and pipelines
RAG applications
Any non-LangGraph agent

Use LangGraph module for:

LangGraph’s create_react_agent
LangGraph workflows

Testing

cd hooks/langchain  # or hooks/langgraph
pip install pytest pytest-asyncio

# Run tests
pytest tests/ -v

Next Steps

CrewAI Integration

Protect multi-agent CrewAI systems

Configure Policies

Create custom guardrail policies

View Metrics

Monitor guardrails performance

Audit Logs

Review security events

​Overview