AI agents call list_functions to retrieve information from Open WebUI MCP Server without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves and enumerates existing functions without creating, modifying, or deleting them. It is a pure read operation that discovers available administrative resources. The low severity reflects minimal blast radius—an AI agent misusing this could at worst enumerate functions to identify targets for other operations, but the tool itself causes no data modification or harm.
From the tool's definition Tool name 'list_functions' and description 'List all functions (filters and pipes)' indicate a query/retrieval operation with no side effects.
Documented attack patterns abuse exactly the kind of access list_functions gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Open WebUI MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for list_functions:
{
"version": "1",
"default": "deny",
"tools": {
"list_functions": {}
}
}list_functions is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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List all functions (filters and pipes). It is categorised as a Read tool in the Open WebUI MCP Server MCP Server, which means it retrieves data without modifying state.
Register the Open WebUI MCP Server MCP server in PolicyLayer and add a rule for list_functions: 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 Open WebUI MCP Server. Nothing to install.
list_functions 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_functions 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_functions. 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_functions is provided by the Open WebUI MCP Server MCP server (troylar/open-webui-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Open WebUI MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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82 Open WebUI MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.