Pre Hook Input

1"""
2Pre Hook Input
3=============================
4
5Example demonstrating how to use a pre_hook to perform comprehensive input validation for your Kern Agent.
6"""
7
8from kern.agent import Agent
9from kern.exceptions import CheckTrigger, InputCheckError
10from kern.models.openai import OpenAIResponses
11from kern.run.agent import RunInput
12from pydantic import BaseModel
13
14
15# ---------------------------------------------------------------------------
16# Create Agent
17# ---------------------------------------------------------------------------
18class InputValidationResult(BaseModel):
19    is_relevant: bool
20    has_sufficient_detail: bool
21    is_safe: bool
22    concerns: list[str]
23    recommendations: list[str]
24
25
26def comprehensive_input_validation(run_input: RunInput) -> None:
27    """
28    Pre-hook: Comprehensive input validation using an AI agent.
29
30    This hook validates input for:
31    - Relevance to the agent's purpose
32    - Sufficient detail for meaningful response
33
34    Could also be used to check for safety, prompt injection, etc.
35    """
36
37    # Input validation agent
38    validator_agent = Agent(
39        name="Input Validator",
40        model=OpenAIResponses(id="gpt-5-mini"),
41        instructions=[
42            "You are an input validation specialist. Analyze user requests for:",
43            "1. RELEVANCE: Ensure the request is appropriate for a financial advisor agent",
44            "2. DETAIL: Verify the request has enough basic information for a meaningful response.",
45            "   A request has sufficient detail if it includes at least a few of: age, income, savings, goals, or risk tolerance.",
46            "   Do NOT require exhaustive information - a reasonable question with some context is sufficient.",
47            "3. SAFETY: Ensure the request is not harmful or unsafe",
48            "",
49            "List specific concerns and recommendations for improvement.",
50            "",
51            "Be lenient with detail checks - if the user provides a clear question with some financial context, mark has_sufficient_detail as true.",
52            "Only mark has_sufficient_detail as false for extremely vague requests like 'help me invest' with no context at all.",
53        ],
54        output_schema=InputValidationResult,
55    )
56
57    validation_result = validator_agent.run(
58        input=f"Validate this user request: '{run_input.input_content}'"
59    )
60
61    result = validation_result.content
62
63    # Check validation results
64    if not result.is_safe:
65        raise InputCheckError(
66            f"Input is harmful or unsafe. {result.recommendations[0] if result.recommendations else ''}",
67            check_trigger=CheckTrigger.INPUT_NOT_ALLOWED,
68        )
69
70    if not result.is_relevant:
71        raise InputCheckError(
72            f"Input is not relevant to financial advisory services. {result.recommendations[0] if result.recommendations else ''}",
73            check_trigger=CheckTrigger.OFF_TOPIC,
74        )
75
76    if not result.has_sufficient_detail:
77        raise InputCheckError(
78            f"Input lacks sufficient detail for a meaningful response. Suggestions: {', '.join(result.recommendations)}",
79            check_trigger=CheckTrigger.INPUT_NOT_ALLOWED,
80        )
81
82
83def main():
84    print("Input Validation Pre-Hook Example")
85    print("=" * 60)
86
87    # Create a financial advisor agent with comprehensive hooks
88    agent = Agent(
89        name="Financial Advisor",
90        model=OpenAIResponses(id="gpt-5-mini"),
91        pre_hooks=[comprehensive_input_validation],
92        description="A professional financial advisor providing investment guidance and financial planning advice.",
93        instructions=[
94            "You are a knowledgeable financial advisor with expertise in:",
95            "• Investment strategies and portfolio management",
96            "• Retirement planning and savings strategies",
97            "• Risk assessment and diversification",
98            "• Tax-efficient investing",
99            "",
100            "Provide clear, actionable advice while being mindful of individual circumstances.",
101            "Always remind users to consult with a licensed financial advisor for personalized advice.",
102        ],
103    )
104
105    # Test 1: Valid financial question (should work normally with enhanced formatting)
106    print("\n[TEST 1] Valid financial question")
107    print("-" * 40)
108    try:
109        response = agent.run(
110            input="""
111            I'm 35 years old and want to start investing for retirement.
112            I can save $1000 per month in addition to my current retirement savings and have moderate risk tolerance.
113            My gross income is $100,000.
114            My current retirement savings in IRAs and 401(k)s is $100,000, my total savings is $200,000, and my net worth is $300,000.
115            My country is the United States.
116
117            Do you have advice for me?
118            """
119        )
120        print("[OK] Success! Response validated by pre-hook:")
121        print(response.content)
122    except Exception as e:
123        print(f"[ERROR] Unexpected error: {e}")
124
125    # Test 2: Input with insufficient detail (should trigger pre-hook)
126    print("\n[TEST 2] Vague input (insufficient detail)")
127    print("-" * 40)
128    try:
129        response = agent.run(input="Help me invest")
130        print(response.content)
131    except InputCheckError as e:
132        print(f"[BLOCKED] Pre-hook validation failed: {e}")
133        print(f"   Trigger: {e.check_trigger}")
134
135    # Test 3: Irrelevant request (should trigger pre-hook)
136    print("\n[TEST 3] Off-topic request")
137    print("-" * 40)
138    try:
139        response = agent.run(input="What's the best pizza recipe?")
140        print(response.content)
141    except InputCheckError as e:
142        print(f"[BLOCKED] Pre-hook validation failed: {e}")
143        print(f"   Trigger: {e.check_trigger}")
144
145    # Test 4: Potentially harmful content (should trigger pre-hook)
146    print("\n[TEST 4] Potentially unsafe content")
147    print("-" * 40)
148    try:
149        response = agent.run(
150            input="How can I manipulate stock prices to make money quickly?"
151        )
152        print(response.content)
153    except InputCheckError as e:
154        print(f"[BLOCKED] Pre-hook validation failed: {e}")
155        print(f"   Trigger: {e.check_trigger}")
156
157
158# ---------------------------------------------------------------------------
159# Run Agent
160# ---------------------------------------------------------------------------
161if __name__ == "__main__":
162    main()

1# Clone and setup repo
2git clone https://github.com/kern-ai/kern.git
3cd kern/cookbook/02_agents/09_hooks
4
5# Create and activate virtual environment
6./scripts/demo_setup.sh
7source .venvs/demo/bin/activate
8
9python pre_hook_input.py