AI agents call sys_uuid to retrieve information from Onion without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
UUID generation is a mathematical/cryptographic operation that produces identifiers. It does not read existing data (no Read stricto sensu), does not modify or create persisted data (not Write), does not execute arbitrary code (not Execute), does not delete anything (not Destructive), and does not move money (not Financial).
From the tool's definition Tool name is 'sys_uuid' and description states '生成 UUID' (generate UUID). UUID generation is a deterministic read-only operation that retrieves/generates unique identifiers without side effects on system state or data.
Attacks that exploit this kind of access
生成 UUID。. It is categorised as a Read tool in the Onion MCP Server, which means it retrieves data without modifying state.
Register the Onion MCP server in PolicyLayer and add a rule for sys_uuid: 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 Onion. Nothing to install.
sys_uuid 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 sys_uuid 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 sys_uuid. 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.
sys_uuid is provided by the Onion MCP server (onion-ai/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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