call_function

Run a function an app declares (manifest.functions) — data in, data out, no UI needed. The body is code the app

SERVEROpen Mcp Apps SOURCE@2nd1st/open-mcp-apps

High RISK CLASS

Category Execute

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/2nd1st-open-mcp-apps/call-function.md

WHAT IT DOES

What call_function does on Open Mcp Apps

AI agents invoke call_function to trigger actions in Open Mcp Apps. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call: builds kicked off, notifications sent, workflows started.

RISK

Why call_function is rated High

Executes arbitrary code declared by apps with unknown effects and capabilities.

From the tool's definition Run a function an app declares, body is code the app

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs call_function safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Open Mcp Apps, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For call_function, this is the rule to start with:

call_function Rate-limited

call_function stays usable, but rate-capped: a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "call_function": {
      "limits": [
        {
          "counter": "call_function_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Open Mcp Apps, apply this rule, and every call_function call is checked against it from then on.

FAQ

Questions about call_function

What does the call_function tool do? +

Run a function an app declares (manifest.functions) — data in, data out, no UI needed. The body is code the app. It is categorised as a Execute tool in the Open Mcp Apps MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on call_function? +

Register the Open Mcp Apps MCP server in PolicyLayer and add a rule for call_function: 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 Mcp Apps. Nothing to install.

What risk level is call_function? +

call_function is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit call_function? +

Yes. Add a rate_limit block to the call_function 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.

How do I block call_function completely? +

Set action: deny in the PolicyLayer policy for call_function. 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.

What MCP server provides call_function? +

call_function is provided by the Open Mcp Apps MCP server (@2nd1st/open-mcp-apps). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

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