AI agents invoke send_dtmf to trigger actions in Telnyx MCP Server. 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.
DTMF tones are used to interact with phone systems during active calls (e.g., navigating IVR menus, entering PINs). This triggers an external operation on an active call. The description is empty, but the name and server context (telephony) strongly suggest this executes an in-call action. Severity is medium as misuse could interact with sensitive phone systems or authorize actions via DTMF.
From the tool's definition Tool name 'send_dtmf' implies sending DTMF (Dual-Tone Multi-Frequency) tones during a call. Description is empty, lowering confidence.
Documented attack patterns abuse exactly the kind of access send_dtmf gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Telnyx MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for send_dtmf:
{
"version": "1",
"default": "deny",
"tools": {
"send_dtmf": {
"limits": [
{
"counter": "send_dtmf_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}send_dtmf 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.
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send_dtmf. It is categorised as a Execute tool in the Telnyx MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Telnyx MCP Server MCP server in PolicyLayer and add a rule for send_dtmf: 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 Telnyx MCP Server. Nothing to install.
send_dtmf is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the send_dtmf 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 send_dtmf. 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.
send_dtmf is provided by the Telnyx MCP Server MCP server (team-telnyx/telnyx-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Telnyx 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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46 Telnyx MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.