> For the complete documentation index, see [llms.txt](https://ai.ortusbooks.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ai.ortusbooks.com/main-components/middleware/guardrail.md).

# GuardrailMiddleware

Block or reject tool invocations by tool name and argument regex policies

Class: `bxModules.bxai.models.middleware.core.GuardrailMiddleware`

Guards tool execution only. It can block specific tools or reject calls whose arguments match forbidden regex patterns.

## Features

* Denylist tool names with `blockedTools`
* Validate arguments per tool with `argPatterns`
* Works with both normalized `toolArgs` and provider-native tool call shapes
* Returns `reject()` with reason when a rule matches

## Constructor

```javascript
middleware = new bxModules.bxai.models.middleware.core.GuardrailMiddleware(
    blockedTools: [ "deleteRecord", "dropTable" ],
    argPatterns : {
        runSQL: [ { query: "^SELECT" } ]
    }
)
```

## Configuration

| Option         | Type   | Default | Description                                                                   |
| -------------- | ------ | ------- | ----------------------------------------------------------------------------- |
| `blockedTools` | array  | `[]`    | Tool names that are always rejected                                           |
| `argPatterns`  | struct | `{}`    | Per-tool regex rules in the form `{ toolName: [ { paramName: "pattern" } ] }` |

## Hooks Used

* `beforeToolCall`

## Example

```javascript
agent = aiAgent(
    tools      : [ runSQLTool, deleteUserTool ],
    middleware : [
        new bxModules.bxai.models.middleware.core.GuardrailMiddleware(
            blockedTools: [ "deleteUser" ],
            argPatterns : {
                runSQL: [
                    { query: "(?i)^\\s*select\\b" },
                    { query: "(?i)drop|truncate|delete" }
                ]
            }
        )
    ]
)
```

## Notes

* Tool-name matching for `blockedTools` is case-insensitive.
* Pattern rules run only for tools present in `argPatterns`.
* This middleware does not sanitize prompt text or model output.


---

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