CallMCP — Phone Call MCP Server

Request Phone Number Purchase

request_number_purchase

DestructiveIdempotent

Buy a specific available phone number for the business from the phone carrier, with the owner's confirmed approval. The carrier bills the number to the business right away. Available numbers come from search_available_numbers. Optionally connects it to agent_id. Returns needs_user_input, needs_approval, pending_approval, executed, denied or unsupported; only executed means the change was made.

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": {
      "phone_number": "<phone_number>",
      "idempotency_key": "<idempotency_key>"
    },
    "name": "request_number_purchase"
  }
}

Input Schema

Name	Required	Description
`actor`	No	Do not set. Kept for older clients; the signed-in connection identifies you.
`reason`	No	Why the change is being made; kept in the audit log.
`dry_run`	No	Check access, inputs and approval without making the change.
`agent_id`	No	Optional: the agent that answers the number.
`authority`	No	Do not set. It cannot approve a change: the owner approves through review_url or by being signed in.
`source_ref`	No	Optional reference for the request, such as a ticket or automation run ID.
`business_id`	No	Business ID. Required when the token can reach more than one business.
`phone_number`	Yes	The number to buy (E.164), from search_available_numbers.
`idempotency_key`	Yes	Required to make the change. Repeating a key returns the first outcome instead of running the change again.
`queue_for_approval`	No	When approval is missing, create a pending approval the owner can accept in the dashboard instead of returning needs_approval.

Output Schema

Name	Required	Description
`code`	No
`error`	No	Present when success is false
`intent`	No
`result`	No
`status`	No
`message`	No
`success`	Yes	Whether the tool completed successfully
`summary`	No
`approval`	No
`request_id`	No
`risk_level`	No
`business_id`	No
`missing_fields`	No

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedNov 12, 2026

changedInput schema / properties / actor / description

Previous value: -"Who is asking: { type: agent|human|system|integration, id, display_name }."New value: +"Do not set. Kept for older clients; the signed-in connection identifies you."

changedInput schema / properties / authority / description

Previous value: -"How the owner approved this exact change: { mode: 'human_confirmed', confirmed_by, confirmed_at, confirmation_ref }. Without it the result is needs_approval and nothing changes."New value: +"Do not set. It cannot approve a change: the owner approves through review_url or by being signed in."

First observedNov 12, 2026

TDQS

A3.9/5.0

Behavior4/5

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

Annotations already declare destructiveHint=true and idempotentHint=true, but the description adds real consequence detail: the carrier bills the number to the business immediately, the owner must have confirmed approval, and only an 'executed' status means the change happened. Enumerating the full status set edges into territory the output schema may already cover, which keeps this 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?

Front-loaded with the action and consequence, then prerequisites, then outcome semantics. Four sentences carry distinct information. The trailing status enumeration is the one part that partly duplicates the output schema and could be trimmed.

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?

For a destructive, approval-gated purchase with ten parameters and nested authority/actor objects, the description covers the essential agent-facing facts: billing is immediate, approval is required, upstream source of the number, and what outcome signals success. The remaining details (multi-business scoping, dry_run, queuing behavior) are fully handled by the 100%-covered schema and the output schema.

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

Parameters3/5

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

Schema coverage is 100%, so every one of the ten parameters is already documented, including dry_run, queue_for_approval, and the do-not-set fields. The description only adds the provenance hint for phone_number and the optional answering-agent meaning of agent_id, so it roughly matches the schema rather than exceeding it.

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

Purpose4/5

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

States a specific verb and resource: buys a named available phone number from the carrier for the business, and notes the optional agent binding. The provenance line ('Available numbers come from search_available_numbers') sharpens the scope. It does not distinguish itself from the similarly named sibling buy_number, so the differentiation is good but not complete.

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

Usage Guidelines4/5

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

Gives clear preconditions and routing: the number must come from search_available_numbers and the purchase requires the owner's confirmed approval. It does not explicitly say when to prefer this over buy_number or request_extra_number, so there is no exclusion guidance, but the usage context is unambiguous.

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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