Captain Hook: AI Agent Policy Enforcement for Claude in SecurityReview.ai

Claude agents today can read from your filesystem, write to it, execute shell commands, call APIs, and interact with external MCP servers. They need that access to function. Stripping it away defeats the purpose of using them.

But once you give a probabilistic system operational authority, you inherit a new class of risk.

Even inside a container or isolated VM, an agent can:

• Access sensitive files within that environment
• Execute destructive commands
• Fetch unapproved external endpoints
• Invoke tools in ways you didn’t anticipate

And then sandboxing isolates, monitoring alerts, and logging explains what happened. But none of them stop an action before it executes.

Today, we’re announcing Captain Hook, an open-source security guardrail within SecurityReview.ai, built for Claude code and Claude agent SDKs to enforce policy on agent behavior before execution.

Within SecurityReview.ai, Captain Hook provides that enforcement layer for teams deploying Claude agents at scale.

Table of Contents

1. The Enforcement Gap in Claude Agents
2. How Captain Hook Enforces Policy on Agent Behavior
3. Build With Agents. Enforce With Policy.

The Enforcement Gap in Claude Agents

Most teams deploying Claude agents already use isolation. Containers. Dedicated VMs. Scoped credentials. That’s necessary, but insufficient.

Agents fail because enforcement happens after execution. Inside an isolated environment, an agent can still perform actions that are perfectly valid from a systems perspective but completely misaligned with intent. Here’s what that looks like in practice:

• An agent reads SSH keys from a developer machine after being prompted to inspect configuration.
• A tool invocation triggers an rm -rf inside a CI container because the agent interpreted reset environment too literally.
• A web fetch tool calls an external endpoint that wasn’t part of the approved integration surface.
• An MCP server performs a destructive action because the agent was instructed to clean up test data.
• A prompt injection payload reframes a legitimate task into a privileged operation the agent is technically allowed to perform.

None of these scenarios require a full system compromise. They require ambiguity. Sandboxing isolates the blast radius, monitoring flags anomalies, and logging helps you investigate. But none of those mechanisms evaluate intent before execution.

The enforcement gap appears at the exact moment an agent decides to call a tool. That’s the point where control must exist, and in most environments, it doesn’t.

How Captain Hook Enforces Policy on Agent Behavior

Within SecurityReview.ai, Captain Hook sits at the decision point where an agent is about to act.

Modern agent frameworks already support hooks, interception points that trigger before or after a tool call. The capability exists, but configuring it across shell scripts and custom handlers quickly becomes operational overhead. In practice, most teams don’t consistently enforce it.

Captain Hook standardizes that enforcement layer.

You define policies in YAML. Those policies translate into pre-execution checks. When an agent attempts to read a file, execute a command, fetch a URL, or call an MCP tool, Captain Hook evaluates the action against defined rules and returns an allow or deny decision before the action runs.

That evaluation is not advisory. It is enforced.

With Captain Hook, you can:

• Restrict file reads and writes by path patterns, including blocking access to sensitive directories.
• Deny destructive shell commands or constrain command execution to approved patterns.
• Enforce network allowlists and explicitly block unapproved external endpoints.
• Reject MCP tool invocations based on defined action patterns, such as blocking delete operations while allowing read access.

These controls apply consistently whether the agent runs on a developer machine, inside CI/CD, or as part of a SecurityReview.ai–monitored workflow. The policy does not depend on how the agent was prompted. It depends on what the agent is attempting to execute.

Captain Hook does not replace sandboxing. If a container restricts access to certain directories, that boundary still holds. Captain Hook operates inside that boundary and evaluates intent at execution time. It reduces reliance on probabilistic alignment and places a deterministic gate in front of high-impact actions.

Build With Agents. Enforce With Policy.

Claude agents are already writing code, modifying infrastructure, and calling external systems inside real environments. That shift is happening faster than most governance models can adapt. If those agents can execute commands and access sensitive resources, you need enforceable boundaries around what they are allowed to do.

Captain Hook is a guardrail framework within SecurityReview.ai, designed to put that enforcement layer in place. You define policies in YAML, and those rules are evaluated before an action executes. Whether it’s a file operation, a shell command, a network call, or an MCP tool invocation. The policy is explicit, version-controlled, and consistently applied across developer machines and CI environments.

Captain Hook is open source and available now as part of the SecurityReview.ai ecosystem. If you’re deploying Claude agents, start by defining what they should never be allowed to execute, and enforce it.