> ## Documentation Index
> Fetch the complete documentation index at: https://praison.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.
# Add Hook • AI Agent SDK
> add_hook: Register a hook callback. Simplified API.
# add\_hook
Function
> This function is defined in the [**registry**](../modules/registry) module.
Register a hook callback. Simplified API.
Accepts both string event names and HookEvent enums:
add\_hook('before\_tool', my\_callback) # String
add\_hook(HookEvent.BEFORE\_TOOL, my\_callback) # Enum
Can also be used as a decorator:
@add\_hook('before\_tool')
def my\_hook(data):
return HookResult.allow()
```mermaid theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
%%{init: {'theme': 'base', 'themeVariables': { 'primaryColor': '#8B0000', 'primaryTextColor': '#fff', 'primaryBorderColor': '#710101', 'lineColor': '#189AB4', 'secondaryColor': '#189AB4', 'tertiaryColor': '#fff' }}}%%
graph TD
event["Event Trigger"] --> hook["Hook: add_hook"]
hook --> decision{"Decision"}
decision -- "Allow" --> proc["Process"]
decision -- "Deny" --> block["Block"]
style hook fill:#189AB4,color:#fff
style event fill:#8B0000,color:#fff
style proc fill:#8B0000,color:#fff
style block fill:#8B0000,color:#fff
```
## Signature
```python theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
def add_hook(event: Union[str, HookEvent], callback: Optional[Callable[[HookInput], HookResult]], priority: int, matcher: Optional[str]) -> Union[str, Callable]
```
## Parameters
Hook event name ('before\_tool', 'after\_llm', etc.) or HookEvent enum
Function to call when hook fires (optional when using as decorator)
Execution order (lower = earlier). Default 10. (Reserved for future use)
Optional regex pattern to match specific targets (e.g., tool names)
### Returns
Hook ID for later removal, or a decorator function if callback is None
### Exceptions
If event string is not a valid HookEvent
## Uses
* `HookEvent`
* `ValueError`
* `register_function`
* `get_default_registry`
## Source
`praisonaiagents/hooks/registry.py` at line 346
***
## Related Documentation