> 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/output-guard.md).

# OutputGuardMiddleware

Redact secrets and strip exfiltration channels from model outputs and reasoning

Class: `bxModules.bxai.models.middleware.security.OutputGuardMiddleware`

Guards outbound model content by redacting sensitive values and removing exfiltration markdown channels.

## Features

* Redacts secrets and PII patterns with configurable mask
* Strips markdown image/link exfiltration patterns with host allowlists
* Scans reasoning content as well as final answer content
* Actions: `redact`, `flag`, `block`
* Optional scan of final agent output in `afterAgentRun`

## Constructor

```javascript
middleware = new bxModules.bxai.models.middleware.security.OutputGuardMiddleware(
    action             : "redact",
    redactors          : [],
    customRedactors    : {},
    mask               : "[REDACTED]",
    stripMarkdownImages: true,
    stripExternalLinks : false,
    allowedImageHosts  : [],
    allowedLinkHosts   : [],
    scanAgentOutput    : true
)
```

## Configuration

| Option                | Type    | Default        | Description                                      |
| --------------------- | ------- | -------------- | ------------------------------------------------ |
| `action`              | string  | `"redact"`     | Behavior on findings: `redact`, `flag`, `block`  |
| `redactors`           | array   | `[]`           | Named redactor set; empty uses default redactors |
| `customRedactors`     | struct  | `{}`           | Extra redactors as regex or closure mappers      |
| `mask`                | string  | `"[REDACTED]"` | Replacement text for redacted values             |
| `stripMarkdownImages` | boolean | `true`         | Strip non-allowlisted markdown images            |
| `stripExternalLinks`  | boolean | `false`        | Rewrite external links to visible text           |
| `allowedImageHosts`   | array   | `[]`           | Allowlist for image hostnames                    |
| `allowedLinkHosts`    | array   | `[]`           | Allowlist for link hostnames                     |
| `scanAgentOutput`     | boolean | `true`         | Also scan final output in `afterAgentRun`        |

## Hooks Used

* `afterLLMCall`
* `afterAgentRun`

## Action Semantics

* `redact`: mutates resolved response fields to scrub detected data
* `flag`: preserves response, logs and records findings
* `block`: throws `BXAI.SecurityViolation`

## Example

```javascript
agent = aiAgent(
    middleware: [
        new bxModules.bxai.models.middleware.security.OutputGuardMiddleware(
            action            : "redact",
            mask              : "[MASKED]",
            stripExternalLinks: true,
            allowedLinkHosts  : [ "docs.ortusbooks.com" ]
        )
    ]
)
```

## Notes

* Invalid actions throw `InvalidAction` at construction.
* Streaming is detection-oriented: `afterLLMCall` runs once the stream has already emitted chunks.
* String-only agent responses cannot always be rewritten in `afterAgentRun`; redaction reliability is strongest at `afterLLMCall`.


---

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