LLM Call Hooks

LLM Call Hooks provide fine-grained control over language model interactions during agent execution. These hooks allow you to intercept LLM calls, modify prompts, transform responses, implement approval gates, and add custom logging or monitoring.

Overview

LLM hooks are executed at two critical points:

• Before LLM Call: Modify messages, validate inputs, or block execution
• After LLM Call: Transform responses, sanitize outputs, or modify conversation history

Hook Types

Before LLM Call Hooks

Executed before every LLM call, these hooks can:

• Inspect and modify messages sent to the LLM
• Block LLM execution based on conditions
• Implement rate limiting or approval gates
• Add context or system messages
• Log request details

Signature:

def before_hook(context: LLMCallHookContext) -> bool | None:
    # Return False to block execution
    # Return True or None to allow execution
    ...

After LLM Call Hooks

Executed after every LLM call, these hooks can:

• Modify or sanitize LLM responses
• Add metadata or formatting
• Log response details
• Update conversation history
• Implement content filtering

Signature:

def after_hook(context: LLMCallHookContext) -> str | None:
    # Return modified response string
    # Return None to keep original response
    ...

LLM Hook Context

The LLMCallHookContext object provides comprehensive access to execution state:

class LLMCallHookContext:
    executor: CrewAgentExecutor  # Full executor reference
    messages: list               # Mutable message list
    agent: Agent                 # Current agent
    task: Task                   # Current task
    crew: Crew                   # Crew instance
    llm: BaseLLM                 # LLM instance
    iterations: int              # Current iteration count
    response: str | None         # LLM response (after hooks only)

Modifying Messages

Important: Always modify messages in-place:

# ✅ Correct - modify in-place
def add_context(context: LLMCallHookContext) -> None:
    context.messages.append({"role": "system", "content": "Be concise"})

# ❌ Wrong - replaces list reference
def wrong_approach(context: LLMCallHookContext) -> None:
    context.messages = [{"role": "system", "content": "Be concise"}]

Registration Methods

1. Global Hook Registration

Register hooks that apply to all LLM calls across all crews:

from crewai.hooks import register_before_llm_call_hook, register_after_llm_call_hook

def log_llm_call(context):
    print(f"LLM call by {context.agent.role} at iteration {context.iterations}")
    return None  # Allow execution

register_before_llm_call_hook(log_llm_call)

2. Decorator-Based Registration

Use decorators for cleaner syntax:

from crewai.hooks import before_llm_call, after_llm_call

@before_llm_call
def validate_iteration_count(context):
    if context.iterations > 10:
        print("⚠️ Exceeded maximum iterations")
        return False  # Block execution
    return None

@after_llm_call
def sanitize_response(context):
    if context.response and "API_KEY" in context.response:
        return context.response.replace("API_KEY", "[REDACTED]")
    return None

3. Crew-Scoped Hooks

Register hooks for a specific crew instance:

@CrewBase
class MyProjCrew:
    @before_llm_call_crew
    def validate_inputs(self, context):
        # Only applies to this crew
        if context.iterations == 0:
            print(f"Starting task: {context.task.description}")
        return None

    @after_llm_call_crew
    def log_responses(self, context):
        # Crew-specific response logging
        print(f"Response length: {len(context.response)}")
        return None

    @crew
    def crew(self) -> Crew:
        return Crew(
            agents=self.agents,
            tasks=self.tasks,
            process=Process.sequential,
            verbose=True
        )

Common Use Cases

1. Iteration Limiting

@before_llm_call
def limit_iterations(context: LLMCallHookContext) -> bool | None:
    max_iterations = 15
    if context.iterations > max_iterations:
        print(f"⛔ Blocked: Exceeded {max_iterations} iterations")
        return False  # Block execution
    return None

2. Human Approval Gate

@before_llm_call
def require_approval(context: LLMCallHookContext) -> bool | None:
    if context.iterations > 5:
        response = context.request_human_input(
            prompt=f"Iteration {context.iterations}: Approve LLM call?",
            default_message="Press Enter to approve, or type 'no' to block:"
        )
        if response.lower() == "no":
            print("🚫 LLM call blocked by user")
            return False
    return None

3. Adding System Context

@before_llm_call
def add_guardrails(context: LLMCallHookContext) -> None:
    # Add safety guidelines to every LLM call
    context.messages.append({
        "role": "system",
        "content": "Ensure responses are factual and cite sources when possible."
    })
    return None

4. Response Sanitization

@after_llm_call
def sanitize_sensitive_data(context: LLMCallHookContext) -> str | None:
    if not context.response:
        return None

    # Remove sensitive patterns
    import re
    sanitized = context.response
    sanitized = re.sub(r'\b\d{3}-\d{2}-\d{4}\b', '[SSN-REDACTED]', sanitized)
    sanitized = re.sub(r'\b\d{4}[- ]?\d{4}[- ]?\d{4}[- ]?\d{4}\b', '[CARD-REDACTED]', sanitized)

    return sanitized

5. Cost Tracking

import tiktoken

@before_llm_call
def track_token_usage(context: LLMCallHookContext) -> None:
    encoding = tiktoken.get_encoding("cl100k_base")
    total_tokens = sum(
        len(encoding.encode(msg.get("content", "")))
        for msg in context.messages
    )
    print(f"📊 Input tokens: ~{total_tokens}")
    return None

@after_llm_call
def track_response_tokens(context: LLMCallHookContext) -> None:
    if context.response:
        encoding = tiktoken.get_encoding("cl100k_base")
        tokens = len(encoding.encode(context.response))
        print(f"📊 Response tokens: ~{tokens}")
    return None

6. Debug Logging

@before_llm_call
def debug_request(context: LLMCallHookContext) -> None:
    print(f"""
    🔍 LLM Call Debug:
    - Agent: {context.agent.role}
    - Task: {context.task.description[:50]}...
    - Iteration: {context.iterations}
    - Message Count: {len(context.messages)}
    - Last Message: {context.messages[-1] if context.messages else 'None'}
    """)
    return None

@after_llm_call
def debug_response(context: LLMCallHookContext) -> None:
    if context.response:
        print(f"✅ Response Preview: {context.response[:100]}...")
    return None

Hook Management

Unregistering Hooks

from crewai.hooks import (
    unregister_before_llm_call_hook,
    unregister_after_llm_call_hook
)

# Unregister specific hook
def my_hook(context):
    ...

register_before_llm_call_hook(my_hook)
# Later...
unregister_before_llm_call_hook(my_hook)  # Returns True if found

Clearing Hooks

from crewai.hooks import (
    clear_before_llm_call_hooks,
    clear_after_llm_call_hooks,
    clear_all_llm_call_hooks
)

# Clear specific hook type
count = clear_before_llm_call_hooks()
print(f"Cleared {count} before hooks")

# Clear all LLM hooks
before_count, after_count = clear_all_llm_call_hooks()
print(f"Cleared {before_count} before and {after_count} after hooks")

Listing Registered Hooks

from crewai.hooks import (
    get_before_llm_call_hooks,
    get_after_llm_call_hooks
)

# Get current hooks
before_hooks = get_before_llm_call_hooks()
after_hooks = get_after_llm_call_hooks()

print(f"Registered: {len(before_hooks)} before, {len(after_hooks)} after")

Advanced Patterns

Conditional Hook Execution

@before_llm_call
def conditional_blocking(context: LLMCallHookContext) -> bool | None:
    # Only block for specific agents
    if context.agent.role == "researcher" and context.iterations > 10:
        return False

    # Only block for specific tasks
    if "sensitive" in context.task.description.lower() and context.iterations > 5:
        return False

    return None

Context-Aware Modifications

@before_llm_call
def adaptive_prompting(context: LLMCallHookContext) -> None:
    # Add different context based on iteration
    if context.iterations == 0:
        context.messages.append({
            "role": "system",
            "content": "Start with a high-level overview."
        })
    elif context.iterations > 3:
        context.messages.append({
            "role": "system",
            "content": "Focus on specific details and provide examples."
        })
    return None

Chaining Hooks

# Multiple hooks execute in registration order

@before_llm_call
def first_hook(context):
    print("1. First hook executed")
    return None

@before_llm_call
def second_hook(context):
    print("2. Second hook executed")
    return None

@before_llm_call
def blocking_hook(context):
    if context.iterations > 10:
        print("3. Blocking hook - execution stopped")
        return False  # Subsequent hooks won't execute
    print("3. Blocking hook - execution allowed")
    return None

Best Practices

1. Keep Hooks Focused: Each hook should have a single responsibility
2. Avoid Heavy Computation: Hooks execute on every LLM call
3. Handle Errors Gracefully: Use try-except to prevent hook failures from breaking execution
4. Use Type Hints: Leverage LLMCallHookContext for better IDE support
5. Document Hook Behavior: Especially for blocking conditions
6. Test Hooks Independently: Unit test hooks before using in production
7. Clear Hooks in Tests: Use clear_all_llm_call_hooks() between test runs
8. Modify In-Place: Always modify context.messages in-place, never replace

Error Handling

@before_llm_call
def safe_hook(context: LLMCallHookContext) -> bool | None:
    try:
        # Your hook logic
        if some_condition:
            return False
    except Exception as e:
        print(f"⚠️ Hook error: {e}")
        # Decide: allow or block on error
        return None  # Allow execution despite error

Type Safety

from crewai.hooks import LLMCallHookContext, BeforeLLMCallHookType, AfterLLMCallHookType

# Explicit type annotations
def my_before_hook(context: LLMCallHookContext) -> bool | None:
    return None

def my_after_hook(context: LLMCallHookContext) -> str | None:
    return None

# Type-safe registration
register_before_llm_call_hook(my_before_hook)
register_after_llm_call_hook(my_after_hook)

Troubleshooting

Hook Not Executing

• Verify hook is registered before crew execution
• Check if previous hook returned False (blocks subsequent hooks)
• Ensure hook signature matches expected type

Message Modifications Not Persisting

• Use in-place modifications: context.messages.append()
• Don’t replace the list: context.messages = []

Response Modifications Not Working

• Return the modified string from after hooks
• Returning None keeps the original response

Conclusion

LLM Call Hooks provide powerful capabilities for controlling and monitoring language model interactions in CrewAI. Use them to implement safety guardrails, approval gates, logging, cost tracking, and response sanitization. Combined with proper error handling and type safety, hooks enable robust and production-ready agent systems.