hook_preset
Install a pre-built JavaScript hook from 20+ built-in presets (eval, atob/btoa, Proxy, Reflect, Object.defineProperty, etc.), or provide customTemplate/customTemplates to install your own reusable hook bodies. Use listPresets=true to see all available preset descriptions.
This record as markdown: /tools/io-github-vmoranv-jshookmcp/hook-preset.md
What hook_preset does on Jshookmcp
AI agents invoke hook_preset to trigger actions in Jshookmcp. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.
Why hook_preset is rated High
Installs JavaScript hooks that intercept and modify runtime execution, enabling arbitrary code effects.
From the tool's definition Install a pre-built JavaScript hook... install your own reusable hook bodies
Attacks that exploit this kind of access
The rule that runs hook_preset safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Jshookmcp, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For hook_preset, this is the rule to start with:
hook_preset stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Jshookmcp, apply this rule, and every hook_preset call is checked against it from then on.
Questions about hook_preset
Install a pre-built JavaScript hook from 20+ built-in presets (eval, atob/btoa, Proxy, Reflect, Object.defineProperty, etc.), or provide customTemplate/customTemplates to install your own reusable hook bodies. Use listPresets=true to see all available preset descriptions. It is categorised as a Execute tool in the Jshookmcp MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Jshook MCP server in PolicyLayer and add a rule for hook_preset: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Jshookmcp. Nothing to install.
hook_preset is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the hook_preset rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for hook_preset. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
hook_preset is provided by the Jshook MCP server (@jshookmcp/jshook). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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