crewAI/docs/edge/en/learn/tool-hooks.mdx

---
title: Tool Call Hooks
description: Learn how to use tool call hooks to intercept, modify, and control tool execution in CrewAI
mode: "wide"
---

Tool Call Hooks provide fine-grained control over tool execution during agent
operations. These hooks allow you to intercept tool calls, modify inputs,
transform outputs, implement safety checks, and add comprehensive logging or
monitoring.

## Overview

Tool hooks are executed at two interception points:

| Point | When | Hook receives |
|-------|------|---------------|
| `PRE_TOOL_CALL` | Before every tool execution | `ToolCallHookContext` |
| `POST_TOOL_CALL` | After every tool execution | `ToolCallHookContext` (with results set) |

Write them with the [`@on` decorator](/learn/execution-hooks). The
[legacy `@before_tool_call` / `@after_tool_call` decorators](#legacy-decorators)
keep working unchanged — both styles register on the same engine and run in one
ordered chain.

## Hook Signature

```python
from crewai.hooks import on, HookAborted, InterceptionPoint, ToolCallHookContext

@on(InterceptionPoint.PRE_TOOL_CALL)
def before_hook(ctx: ToolCallHookContext) -> None:
    # Mutate ctx.tool_input in place, or
    # raise HookAborted(reason, source) to block the call
    ...

@on(InterceptionPoint.POST_TOOL_CALL)
def after_hook(ctx: ToolCallHookContext) -> str | None:
    # Return a string to replace ctx.tool_result
    # Return None to keep the original result
    ...
```

Unlike the boundary and step points, the tool-call points pass the rich
`ToolCallHookContext` directly as the hook argument (there is no separate
`ctx.payload`): mutate `ctx.tool_input` in place before the call, and return a
string to replace the result after it.

When a call is blocked, the tool does not run and the agent receives
`"Tool execution blocked by hook. Tool: <name>"` as the result — the run
continues. `POST_TOOL_CALL` hooks still fire on blocked calls, so monitoring
hooks see every attempt.

## Tool Hook Context

The `ToolCallHookContext` object provides comprehensive access to tool
execution state:

```python
class ToolCallHookContext:
    tool_name: str                    # Name of the tool being called
    tool_input: dict[str, Any]        # Mutable tool input parameters
    tool: CrewStructuredTool          # Tool instance reference
    agent: Agent | BaseAgent | None   # Agent executing the tool
    task: Task | None                 # Current task
    crew: Crew | None                 # Crew instance
    tool_result: str | None           # Agent-facing result string (POST_TOOL_CALL only)
    raw_tool_result: Any | None       # Raw Python result (POST_TOOL_CALL only)
```

For typed tool outputs, `tool_result` is the string the agent sees. By default,
this is JSON. If the tool uses custom formatting, it can be Markdown or another
string. Use `raw_tool_result` when your hook needs the typed object or
dictionary; it is not affected by result replacement.

The context also exposes `request_human_input(prompt, default_message)`, which
pauses live console updates and collects input from the terminal — useful for
approval gates.

### Modifying Tool Inputs

**Important:** Always modify tool inputs in-place:

```python
# ✅ Correct - modify in-place
@on(InterceptionPoint.PRE_TOOL_CALL)
def sanitize_input(ctx: ToolCallHookContext) -> None:
    ctx.tool_input['query'] = ctx.tool_input['query'].lower()

# ❌ Wrong - replaces dict reference; the tool never sees it
@on(InterceptionPoint.PRE_TOOL_CALL)
def wrong_approach(ctx: ToolCallHookContext) -> None:
    ctx.tool_input = {'query': 'new query'}
```

## Registration Methods

### 1. Global Hooks

Apply to all tool calls across all crews. Use `tools=` / `agents=` filters to
scope a hook:

```python
from crewai.hooks import on, HookAborted, InterceptionPoint

@on(InterceptionPoint.PRE_TOOL_CALL)
def log_tool_call(ctx):
    print(f"Tool: {ctx.tool_name}, input: {ctx.tool_input}")

@on(InterceptionPoint.PRE_TOOL_CALL, tools=["delete_file", "drop_table"])
def block_destructive(ctx):
    raise HookAborted(reason=f"{ctx.tool_name} is not allowed", source="safety-policy")

@on(InterceptionPoint.POST_TOOL_CALL, tools=["web_search"], agents=["Researcher"])
def log_search_results(ctx):
    print(f"search returned {len(ctx.tool_result or '')} chars")
```

### 2. Crew-Scoped Hooks

Apply the same decorator to a method inside a `@CrewBase` class to scope the
hook to that crew only:

```python
from crewai.hooks import on, InterceptionPoint

@CrewBase
class MyProjCrew:
    @on(InterceptionPoint.PRE_TOOL_CALL)
    def validate_tool_inputs(self, ctx):
        # Only applies to this crew
        if ctx.tool_name == "web_search" and not ctx.tool_input.get("query"):
            raise HookAborted(reason="empty search query", source="input-validation")

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

## Common Use Cases

### 1. Safety Guardrails

```python
@on(InterceptionPoint.PRE_TOOL_CALL)
def safety_check(ctx: ToolCallHookContext) -> None:
    destructive = {'delete_file', 'drop_table', 'remove_user', 'system_shutdown'}
    if ctx.tool_name in destructive:
        raise HookAborted(reason=f"{ctx.tool_name} is destructive", source="safety-policy")
```

### 2. Human Approval Gate

```python
@on(InterceptionPoint.PRE_TOOL_CALL, tools=["send_email", "make_purchase", "delete_file"])
def require_approval(ctx: ToolCallHookContext) -> None:
    response = ctx.request_human_input(
        prompt=f"Approve {ctx.tool_name}?",
        default_message=f"Input: {ctx.tool_input}\nType 'yes' to approve:",
    )
    if response.lower() != 'yes':
        raise HookAborted(reason="denied by operator", source="approval-gate")
```

### 3. Input Validation and Sanitization

```python
@on(InterceptionPoint.PRE_TOOL_CALL, tools=["web_search"])
def validate_query(ctx: ToolCallHookContext) -> None:
    query = ctx.tool_input.get('query', '')
    if len(query) < 3:
        raise HookAborted(reason="search query too short", source="input-validation")
    ctx.tool_input['query'] = query.strip().lower()

@on(InterceptionPoint.PRE_TOOL_CALL, tools=["read_file"])
def validate_path(ctx: ToolCallHookContext) -> None:
    path = ctx.tool_input.get('path', '')
    if '..' in path or path.startswith('/'):
        raise HookAborted(reason="invalid file path", source="input-validation")
```

### 4. Result Sanitization

```python
import re

@on(InterceptionPoint.POST_TOOL_CALL)
def sanitize_sensitive_data(ctx: ToolCallHookContext) -> str | None:
    if not ctx.tool_result:
        return None
    result = re.sub(
        r'(api[_-]?key|token)["\']?\s*[:=]\s*["\']?[\w-]+',
        r'\1: [REDACTED]',
        ctx.tool_result,
        flags=re.IGNORECASE,
    )
    return re.sub(
        r'\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b',
        '[EMAIL-REDACTED]',
        result,
    )
```

### 5. Tool Usage Analytics

```python
import time
from collections import defaultdict

tool_stats = defaultdict(lambda: {'count': 0, 'total_time': 0})

@on(InterceptionPoint.PRE_TOOL_CALL)
def start_timer(ctx: ToolCallHookContext) -> None:
    ctx.tool_input['_start_time'] = time.time()

@on(InterceptionPoint.POST_TOOL_CALL)
def track_tool_usage(ctx: ToolCallHookContext) -> None:
    start_time = ctx.tool_input.pop('_start_time', time.time())
    tool_stats[ctx.tool_name]['count'] += 1
    tool_stats[ctx.tool_name]['total_time'] += time.time() - start_time
```

### 6. Rate Limiting

```python
from collections import defaultdict
from datetime import datetime, timedelta

tool_call_history = defaultdict(list)

@on(InterceptionPoint.PRE_TOOL_CALL)
def rate_limit_tools(ctx: ToolCallHookContext) -> None:
    now = datetime.now()
    history = tool_call_history[ctx.tool_name]
    history[:] = [t for t in history if now - t < timedelta(minutes=1)]
    if len(history) >= 10:
        raise HookAborted(reason=f"rate limit exceeded for {ctx.tool_name}",
                          source="rate-limiter")
    history.append(now)
```

## Hook Management

```python
from crewai.hooks import (
    InterceptionPoint,
    clear_all_hooks,
    clear_hooks,
    get_hooks,
    unregister_hook,
)

# Unregister a specific hook
unregister_hook(InterceptionPoint.PRE_TOOL_CALL, my_hook)

# Clear one point, or everything (e.g. between tests)
clear_hooks(InterceptionPoint.POST_TOOL_CALL)
clear_all_hooks()

# Inspect what's registered
print(len(get_hooks(InterceptionPoint.PRE_TOOL_CALL)))
```

The legacy management API (`register_before_tool_call_hook`,
`unregister_before_tool_call_hook`, `clear_before_tool_call_hooks`,
`clear_all_tool_call_hooks`, `get_before_tool_call_hooks`, and their `after_`
counterparts) operates on the same underlying registries, so either API can
manage hooks registered by the other.

## Legacy Decorators

The original per-point decorators keep working unchanged and run in the same
registration-order chain as `@on` hooks:

```python
from crewai.hooks import before_tool_call, after_tool_call

@before_tool_call
def block_dangerous_tools(context):
    if context.tool_name in ('delete_database', 'drop_table'):
        return False  # Block execution
    return None

@after_tool_call(tools=["web_search"])
def sanitize_results(context):
    if context.tool_result and "password" in context.tool_result.lower():
        return context.tool_result.replace("password", "[REDACTED]")
    return None
```

Differences from `@on`:

- **Blocking** is `return False` from a before hook — equivalent to raising
  `HookAborted`, but without a custom reason or source for telemetry. The agent
  sees the same `"Tool execution blocked by hook"` message.
- **Signatures** are point-specific: before hooks return `bool | None`, after
  hooks return `str | None`. The context object is the same
  `ToolCallHookContext`.
- **Filters and crew-scoping** work the same way:
  `@before_tool_call(tools=[...], agents=[...])`, and applying the decorator to
  a `@CrewBase` method scopes it to that crew.

Prefer `@on` for new code; keep the legacy style where it is already in use —
there is no behavioral penalty.

## Best Practices

1. **Keep hooks focused and fast** — they run on every tool call
2. **Modify in-place** — always mutate `ctx.tool_input`, never replace the dict
3. **Prefer filters over conditionals** — `tools=` / `agents=` keep hook bodies small
4. **Abort loudly** — raise `HookAborted` with a meaningful reason and source;
   any other exception is swallowed (fail-open)
5. **Use type hints** — annotate with `ToolCallHookContext` for IDE support
6. **Clear hooks in tests** — call `clear_all_hooks()` between test runs

## Troubleshooting

### Hook Not Executing
- Verify the hook is registered before crew execution
- Check whether an earlier hook blocked the call (subsequent pre hooks don't run)
- Check `tools=` / `agents=` filters against the actual tool name and agent role

### Input Modifications Not Working
- Use in-place modifications: `ctx.tool_input['key'] = value`
- Don't replace the dict: `ctx.tool_input = {}`

### Result Modifications Not Working
- Return the modified string from a `POST_TOOL_CALL` hook
- Returning `None` keeps the original result

### Tool Blocked Unexpectedly
- Check all pre hooks for `HookAborted` / `return False` conditions
- The abort reason and source appear on the `HookDispatchedEvent` telemetry

## Related Documentation

- [Execution Hooks Overview →](/learn/execution-hooks)
- [LLM Call Hooks →](/learn/llm-hooks)
- [Execution Boundary Hooks →](/learn/execution-boundary-hooks)
- [Step Hooks →](/learn/step-hooks)