AI agents use set_opacity to create or update resources in Figma AI Bridge — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Figma AI Bridge environment.
This tool modifies design data (node opacity) in a Figma document, making it a Write operation rather than Read. The change is reversible (opacity can be adjusted back to original values), so it does not qualify as Destructive. The severity is medium because while misuse could alter designs, the blast radius is limited to visual property changes on a single node, without data deletion or workflow disruption.
From the tool's definition Tool description states it 'Set[s] the opacity of a node in Figma', which modifies a design property. The Figma AI Bridge context confirms it enables 'design creation, editing' operations. Opacity is a reversible visual property that can be changed back.
Documented attack patterns abuse exactly the kind of access set_opacity gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Figma AI Bridge, and nothing reaches the server without passing your rules. This is the rule we recommend for set_opacity:
{
"version": "1",
"default": "deny",
"tools": {
"set_opacity": {
"limits": [
{
"counter": "set_opacity_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}set_opacity 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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Set the opacity of a node in Figma. It is categorised as a Write tool in the Figma AI Bridge MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the Figma AI Bridge MCP server in PolicyLayer and add a rule for set_opacity: 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 Figma AI Bridge. Nothing to install.
set_opacity 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 set_opacity 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 set_opacity. 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.
set_opacity is provided by the Figma AI Bridge MCP server (renfei-design/figma_ai_bridge). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Figma AI Bridge, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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64 Figma AI Bridge tools catalogued and risk-classified — across an index of 43,000+ MCP servers.