AI agents call sys_json_valid 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.
This tool only performs syntactic validation and formatting of JSON input data. It retrieves or transforms data without creating, modifying, deleting, or executing any operations. The output is derived purely from the input; no external state is changed. This is a classic Read category operation.
From the tool's definition Tool name 'sys_json_valid' and description 'validates JSON strings for legality and returns formatted results' indicate a validation/parsing operation with no side effects.
Attacks that exploit this kind of access
验证 JSON 字符串是否合法，并返回格式化后的结果。. 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_json_valid: 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_json_valid 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_json_valid 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_json_valid. 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_json_valid 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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