crewAI/docs/v1.15.5/en/learn/execution-hooks.mdx

---
title: Execution Hooks
description: Intercept, modify, and control CrewAI's runtime with the @on decorator - one contract covering every interception point
mode: "wide"
---

Execution hooks provide fine-grained control over the runtime behavior of your
CrewAI agents. Unlike kickoff hooks that run before and after crew execution,
execution hooks intercept specific operations during execution — from the moment
a run starts, through every model call, tool call, and task or flow-method step,
down to the final output.

Hooks are written with the `@on` decorator: one registration API and one
contract cover every interception point in the framework.

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

@on(InterceptionPoint.PRE_TOOL_CALL, tools=["delete_file"])
def guard_deletes(ctx):
    raise HookAborted(reason="file deletion is not allowed", source="policy")
```

<Note>
The point-specific decorators (`@before_llm_call`, `@after_tool_call`, ...) keep
working unchanged — they are adapters over the same engine. See
[Point-specific decorators (legacy)](#point-specific-decorators-legacy) at the
end of this page.
</Note>

## The contract

Every hook is a **synchronous** callable that receives a single typed context:

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

@on(InterceptionPoint.INPUT)
def add_defaults(ctx):
    # 1. Observe: read anything off the context.
    # 2. Mutate in place: change ctx.payload or nested fields directly.
    ctx.payload.setdefault("locale", "en-US")
    # 3. Or replace: return a new value to swap ctx.payload.
    # 4. Or abort: raise HookAborted(reason, source) to stop the operation.
    return None
```

A hook may do any of four things:

| Action | How | Effect |
|--------|-----|--------|
| **Proceed** | `return None` (or nothing) | Operation continues unchanged |
| **Mutate** | Change `ctx.payload` / fields in place | Change is visible downstream |
| **Replace** | `return new_payload` | A non-`None` return replaces `ctx.payload` |
| **Abort** | `raise HookAborted(reason, source)` | Operation is stopped; the reason propagates |

## Registering hooks

Use `@on` for global hooks. It accepts `agents=` / `tools=` filters to scope a
hook to specific agent roles or tool names:

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

@on(InterceptionPoint.POST_TOOL_CALL, agents=["researcher"], tools=["web_search"])
def log_search_results(ctx):
    print(f"search returned: {(ctx.tool_result or '')[:80]}")
```

Applied to a method inside a `@CrewBase` class, `@on` registers a
**crew-scoped** hook, active only while that crew runs:

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

@CrewBase
class MyProjCrew:
    @on(InterceptionPoint.PRE_MODEL_CALL)
    def validate_inputs(self, ctx):
        # Only applies to this crew
        return None
```

## Interception point catalog

Each family has a detailed guide covering its context schema, payload
semantics, and examples.

### [Execution boundaries](/edge/en/learn/execution-boundary-hooks)

| Point | When | `ctx.payload` |
|-------|------|---------------|
| `EXECUTION_START` | A crew or flow is about to begin | inputs `dict` |
| `INPUT` | Resolved inputs for the execution | inputs `dict` |
| `OUTPUT` | Final result is ready | the output object |
| `EXECUTION_END` | A crew or flow has finished | the output object |

### [Model boundaries](/edge/en/learn/llm-hooks) & [tool boundaries](/edge/en/learn/tool-hooks)

| Point | When | Hook receives |
|-------|------|---------------|
| `PRE_MODEL_CALL` | Before an LLM call | `LLMCallHookContext` |
| `POST_MODEL_CALL` | After an LLM call | `LLMCallHookContext` (with `response` set) |
| `PRE_TOOL_CALL` | Before a tool runs | `ToolCallHookContext` |
| `POST_TOOL_CALL` | After a tool runs | `ToolCallHookContext` (with results set) |

At these four points the hook receives the rich legacy context **directly** as
its argument — there is no separate `ctx.payload`. Mutate `ctx.messages` /
`ctx.tool_input` in place, and return a string from a post hook to replace the
response / tool result.

### [Step points](/edge/en/learn/step-hooks)

| Point | When | `ctx.payload` |
|-------|------|---------------|
| `PRE_STEP` | Before a task or flow-method step | step input |
| `POST_STEP` | After a task or flow-method step | step output |

`PRE_STEP` / `POST_STEP` carry `ctx.kind` (`"task"` or `"flow_method"`) and
`ctx.step_name`.

## Aborting an operation

`HookAborted` carries a `reason` and an optional `source`. The `source` defaults
to the aborting hook when omitted, which is useful for telemetry and failure
messages:

```python
@on(InterceptionPoint.EXECUTION_START)
def enforce_policy(ctx):
    if not ctx.payload.get("authorized"):
        raise HookAborted(reason="unauthorized execution", source="access-control")
```

## Composition, ordering, and fail-open

- Multiple hooks on the same point run in **registration order**, global hooks
  first, then execution-scoped hooks. Legacy hooks registered for the same point
  participate in the same chain.
- The (possibly mutated) payload flows from one hook to the next.
- `HookAborted` **propagates by design** and stops the chain.
- Any *other* exception raised by a hook is **swallowed** (fail-open) so a single
  buggy hook can't crash a run.
- When no hook is registered for a point, dispatch is a single dict lookup
  (no-op fast path), so unused points cost effectively nothing.

## Common patterns

### Safety guardrails

```python
@on(InterceptionPoint.PRE_TOOL_CALL)
def block_dangerous_tools(ctx):
    dangerous = {"delete_file", "drop_table", "system_shutdown"}
    if ctx.tool_name in dangerous:
        raise HookAborted(reason=f"{ctx.tool_name} is blocked", source="safety-policy")

@on(InterceptionPoint.PRE_MODEL_CALL)
def iteration_limit(ctx):
    if ctx.iterations > 15:
        raise HookAborted(reason="maximum iterations exceeded", source="loop-guard")
```

### Human-in-the-loop approval

```python
@on(InterceptionPoint.PRE_TOOL_CALL, tools=["send_email", "make_payment"])
def require_approval(ctx):
    response = ctx.request_human_input(
        prompt=f"Approve {ctx.tool_name}?",
        default_message="Type 'yes' to approve:",
    )
    if response.lower() != "yes":
        raise HookAborted(reason="rejected by operator", source="approval-gate")
```

### Sanitizing outputs

A non-`None` return value replaces the interceptable value, so transformations
are plain return statements:

```python
import re

@on(InterceptionPoint.POST_MODEL_CALL)
def redact_keys(ctx):
    return re.sub(
        r'(api[_-]?key)["\']?\s*[:=]\s*["\']?[\w-]+',
        r"\1: [REDACTED]",
        ctx.response,
        flags=re.IGNORECASE,
    )
```

### Observing steps

```python
@on(InterceptionPoint.POST_STEP)
def trace_steps(ctx):
    print(f"{ctx.kind} '{ctx.step_name}' finished")
```

## Telemetry

Whenever a point actually dispatches to at least one hook, CrewAI emits a
`HookDispatchedEvent` on the event bus with the point, the outcome
(`proceeded` / `modified` / `aborted`), the hook count, the duration, and — for
aborts — the reason and source. The no-op fast path emits nothing.

## Managing hooks in tests

Global hooks persist for the lifetime of the process. Reset them between tests:

```python
import pytest
from crewai.hooks import clear_all_hooks

@pytest.fixture(autouse=True)
def reset_hooks():
    clear_all_hooks()
    yield
    clear_all_hooks()
```

## Best practices

1. **Keep hooks focused** — one clear responsibility per hook; register several
   small hooks rather than one that does everything.
2. **Keep hooks fast** — hooks run on every dispatch of their point; avoid heavy
   computation and lazy-import heavy dependencies.
3. **Prefer scoping** — use `agents=` / `tools=` filters and crew-scoped
   registration instead of unconditional global hooks.
4. **Abort loudly** — raise `HookAborted` with a meaningful `reason` and
   `source`; that context surfaces in error messages and telemetry. Remember
   that any other exception is swallowed (fail-open), so don't rely on raising
   `ValueError` to stop a run.

## Point-specific decorators (legacy)

Before `@on`, LLM and tool calls were hooked with dedicated decorator pairs.
These keep working unchanged — they are adapters over the same dispatcher, so
they compose with `@on` hooks in the same registration-order chain:

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

@before_llm_call
def limit_iterations(context):
    if context.iterations > 10:
        return False  # Block execution

@after_tool_call
def log_tool_result(context):
    print(f"Tool {context.tool_name} completed")
```

Differences from `@on`:

- They cover **only** the four model/tool points — no execution boundaries, no
  steps.
- Blocking is `return False`, with no abort reason or source attached.
- They receive the same rich contexts — `LLMCallHookContext` (with full
  executor access) and `ToolCallHookContext` — that `@on` hooks receive at the
  model/tool points.
- Crew-scoping works the same way: apply the decorator to a method inside a
  `@CrewBase` class.
- They support the same `agents=` / `tools=` filters.

You might still prefer them for existing codebases that already use
`return False` semantics, or when you want the point-specific typed signatures.
For the detailed guides — context attributes, patterns, and management APIs
(`register_*` / `unregister_*` / `clear_*`) — see:

- [LLM Call Hooks →](/edge/en/learn/llm-hooks)
- [Tool Call Hooks →](/edge/en/learn/tool-hooks)

## Related documentation

- [Before and After Kickoff Hooks →](/edge/en/learn/before-and-after-kickoff-hooks)
- [Human-in-the-Loop →](/edge/en/learn/human-in-the-loop)