Evaluates a JavaScript expression in the React Native application context using CDP Runtime.evaluate and returns the result value. If you need to require a module, use __r function.
AI agents call evaluate-javascript to retrieve information from React Native DevTools MCP without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
Even though evaluate-javascript only reads data, uncontrolled read access leaks sensitive information and racks up API costs — an agent caught in a retry loop can make thousands of calls a minute without anyone noticing.
Attacks that exploit this kind of access
Evaluates a JavaScript expression in the React Native application context using CDP Runtime.evaluate and returns the result value. If you need to require a module, use __r function. It is categorised as a Read tool in the React Native DevTools MCP MCP Server, which means it retrieves data without modifying state.
Register the React Native DevTools MCP server in PolicyLayer and add a rule for evaluate-javascript: 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 React Native DevTools MCP. Nothing to install.
evaluate-javascript is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the evaluate-javascript 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 evaluate-javascript. 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.
evaluate-javascript is provided by the React Native DevTools MCP server (v3ron/react-native-devtools-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.