Virtnumber

Send an SMS

send_sms

Destructive

Send an SMS from one of the account's numbers (plans with canSendSms). Charges the price per SMS from the balance: one SMS is up to 160 characters, or 70 with non-Latin characters; a longer text is billed as several SMS.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "number": "<number>",
      "to": "<to>",
      "text": "<text>"
    },
    "name": "send_sms"
  }
}

Input Schema

Name	Required	Description
`to`	Yes	Destination phone number in international format
`text`	Yes
`number`	Yes	The account's number to send from
`idempotency_key`	No	Any unique string (e.g. a UUID). Repeating a call with the same key returns the first result instead of acting twice.

Output Schema

Name	Required	Description	Default
`id`	Yes
`to`	Yes
`priceEur`	Yes
`segments`	Yes

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 8, 2026

TDQS

A4.1/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already flag destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description adds real economic behavior the annotations cannot express: the per-SMS charge against balance and the 160/70-character segmentation rule that makes long texts bill as multiple messages. It does not mention that sending is irreversible or how the idempotency_key relates to the declared non-idempotent hint, which keeps it from a 5.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness4/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single sentence, front-loaded with the action and sender constraint, then cost implications. The parenthetical and semicolon chain make it slightly dense to parse, but every clause carries information an agent needs before calling.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return values need not be described. For a mutation tool with billing consequences, the description covers eligibility, cost, and segmentation. What is missing is delivery semantics — whether the call confirms delivery or merely queues, which matters given the wait_for_sms sibling.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 75%, and notably the 'text' parameter has no schema description at all — the description compensates by explaining character limits, the non-Latin 70-character threshold, and multi-segment billing. It also reinforces that 'number' must be an account-owned sender. It says nothing extra about 'to' formatting or the idempotency_key beyond what the schema already documents.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource ('Send an SMS') plus the sender constraint ('from one of the account's numbers') and the plan gate ('plans with canSendSms'). No sibling in the list sends messages, so this is immediately distinguishable from list_messages, wait_for_sms, and the number-management tools.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

The parenthetical '(plans with canSendSms)' gives an eligibility precondition, which is useful. However, it never states when to prefer this over alternatives or what to do afterwards (e.g., that wait_for_sms is the receiving counterpart), so usage is only implied.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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