Query native UI/accessibility tree. Large payload. Cannot see inside WebView content. Prefer query_selector for RN elements, webview_evaluate_script for WebView DOM.
AI agents call describe_ui to retrieve information from React Native without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
describe_ui performs read-only introspection of the app's UI and accessibility tree. It queries existing state without creating, modifying, deleting, or executing arbitrary operations. The large payload and accessibility tree retrieval are data retrieval operations with no side effects.
From the tool's definition Tool is described as 'Query native UI/accessibility tree' and explicitly recommends using alternative tools for other use cases, indicating it only retrieves UI structure without modification.
Attacks that exploit this kind of access
Query native UI/accessibility tree. Large payload. Cannot see inside WebView content. Prefer query_selector for RN elements, webview_evaluate_script for WebView DOM. It is categorised as a Read tool in the React Native MCP Server, which means it retrieves data without modifying state.
Register the React Native MCP server in PolicyLayer and add a rule for describe_ui: 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. Nothing to install.
describe_ui 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 describe_ui 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 describe_ui. 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.
describe_ui is provided by the React Native MCP server (@ohah/react-native-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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