Write a value to a device property.
AI agents use write_property to create or update resources in Wot — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Wot environment.
This tool creates or modifies data on IoT devices in a reversible manner. While the severity depends on what properties are exposed (e.g., writing to a thermostat is low-risk; writing to a door lock is higher-risk), the tool itself fits the Write category.
From the tool's definition Tool name 'write_property' and description 'Write a value to a device property' explicitly indicate modification of device state. The action is reversible (a property can be written again with a different value), distinguishing it from destructive operations.
Documented attack patterns abuse exactly the kind of access write_property gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Wot, and nothing reaches the server without passing your rules. This is the rule we recommend for write_property:
{
"version": "1",
"default": "deny",
"tools": {
"write_property": {
"limits": [
{
"counter": "write_property_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}write_property stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Write a value to a device property. It is categorised as a Write tool in the Wot MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Wot MCP server in PolicyLayer and add a rule for write_property: 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 Wot. Nothing to install.
write_property is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the write_property 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 write_property. 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.
write_property is provided by the Wot MCP server (macc-n/wot-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Wot, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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4 Wot tools catalogued and risk-classified — across an index of 43,000+ MCP servers.