execute_js
Run JS in a sandbox, capture output (300 sats/call; free tier 100 calls/mo)
This record as markdown: /tools/com-thetempleofdoom-hyperion-hyperion/execute-js.md
What execute_js does on Hyperion
AI agents invoke execute_js to trigger actions in Hyperion. 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.
| Parameter | Type | Required | Description |
|---|---|---|---|
code | string | Yes | JavaScript expression or script snippet. |
Parameters from the server's own tool schema.
Why execute_js is rated High
execute_js triggers real processes with real consequences. An agent gone sideways doesn't fire it once. It starts dozens of builds, sends mass notifications, or burns through compute before anyone looks up.
Risk signalsAccepts freeform code/query input (code)
Attacks that exploit this kind of access
The rule that runs execute_js safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Hyperion, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For execute_js, this is the rule to start with:
execute_js 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 Hyperion, apply this rule, and every execute_js call is checked against it from then on.
Questions about execute_js
Run JS in a sandbox, capture output (300 sats/call; free tier 100 calls/mo). It is categorised as a Execute tool in the Hyperion MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
execute_js accepts 1 parameter: code. Required: code. The full parameter table on this page comes from the server's own tool schema.
Register the Hyperion MCP server in PolicyLayer and add a rule for execute_js: 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 Hyperion. Nothing to install.
execute_js 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 execute_js 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 execute_js. 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.
execute_js is provided by the Hyperion MCP server (https://hyperion.thetempleofdoom.com/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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