read_input_registers
AI agents call read_input_registers to retrieve information from Modbus without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves data from Modbus input registers without modifying state. While the description is empty (lowering confidence slightly), the name and context are clear. Severity is medium rather than low because Modbus controls physical infrastructure; unauthorized reads could expose sensitive operational data or enable reconnaissance for attacks on critical systems.
From the tool's definition Tool name 'read_input_registers' indicates a read operation on Modbus input registers. Modbus is an industrial control protocol commonly used in critical infrastructure (power systems, manufacturing, etc.).
Documented attack patterns abuse exactly the kind of access read_input_registers gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Modbus, and nothing reaches the server without passing your rules. This is the rule we recommend for read_input_registers:
{
"version": "1",
"default": "deny",
"tools": {
"read_input_registers": {}
}
}read_input_registers is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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read_input_registers. It is categorised as a Read tool in the Modbus MCP Server, which means it retrieves data without modifying state.
Register the Modbus MCP server in PolicyLayer and add a rule for read_input_registers: 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 Modbus. Nothing to install.
read_input_registers 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 read_input_registers 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 read_input_registers. 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.
read_input_registers is provided by the Modbus MCP server (kukapay/modbus-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Modbus, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
6 Modbus tools catalogued and risk-classified — across an index of 43,000+ MCP servers.