List available node classes for a provider.service combo. Args: provider: Provider name (e.g. 'aws', 'gcp', 'k8s'). service: Service category (e.g. 'compute', 'database', 'network'). Returns: List of nodes with keys: name, import, alias_of (optional).
Part of the Diagrams MCP server.
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AI agents call list_nodes to retrieve information from Diagrams MCP without modifying any data. This is common in research, monitoring, and reporting workflows where the agent needs context before taking action. Because read operations don't change state, they are generally safe to allow without restrictions -- but you may still want rate limits to control API costs.
Even though list_nodes only reads data, uncontrolled read access can leak sensitive information or rack up API costs. An agent caught in a retry loop could make thousands of calls per minute. A rate limit gives you a safety net without blocking legitimate use.
Read-only tools are safe to allow by default. No rate limit needed unless you want to control costs.
{
"version": "1",
"default": "deny",
"tools": {
"list_nodes": {}
}
}See the full Diagrams MCP policy for all 9 tools.
These attack patterns abuse exactly the kind of access list_nodes gives an agent. Each links to the full case and the policy that stops it:
Other read tools across the catalogue. The same approach applies to each: allow, with a rate cap to control cost.
List available node classes for a provider.service combo. Args: provider: Provider name (e.g. 'aws', 'gcp', 'k8s'). service: Service category (e.g. 'compute', 'database', 'network'). Returns: List of nodes with keys: name, import, alias_of (optional).. It is categorised as a Read tool in the Diagrams MCP MCP Server, which means it retrieves data without modifying state.
Register the Diagrams MCP server in PolicyLayer and add a rule for list_nodes: 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 Diagrams MCP. Nothing to install.
list_nodes 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 list_nodes 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 list_nodes. 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.
list_nodes is provided by the Diagrams MCP server (pypi:diagrams-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 9 Diagrams MCP tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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