CallMCP — Phone Call MCP Server

Search Available Numbers

search_available_numbers

Read-only

Search the carrier for phone numbers available to purchase (live number inventory). In the acquisition flow this follows set_owner_phone, which saves a reachable owner number or records a decline.

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "search_available_numbers"
  }
}

Input Schema

Name	Required	Description
`limit`	No	Max results to return (default 10, max 20).
`country`	No	Two-letter country code (default US).
`area_code`	No	Preferred area code (optional).
`business_id`	No	Search that business's carrier inventory (optional; defaults to the platform carrier).

Output Schema

Name	Required	Description
`error`	No	Present when success is false
`success`	Yes	Whether the tool completed successfully
`available_numbers`	No

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 12, 2026

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=false and destructiveHint=false, covering the safety profile. The description adds useful behavioral context by noting the inventory is 'live' on the carrier, which explains why results are not stable or repeatable. It does not mention latency, cost, rate limits, or how quickly a returned number can be lost.

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

Conciseness5/5

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

Two sentences with no filler, and the core purpose is front-loaded before the flow-position note. Every clause carries information the agent needs.

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-value explanation is unnecessary, and the description covers purpose, data source (carrier live inventory, platform vs business), and flow position. What remains thin — freshness or availability guarantees for numbers found — is minor for a read-only search.

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 description coverage is 100%, so limit, country, area_code, and business_id are already fully documented, including the default to the platform carrier. The description adds no parameter-level meaning beyond what the schema states, so the baseline 3 applies.

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?

The description gives a precise verb and resource — searching the carrier for numbers available to purchase — and the parenthetical 'live number inventory' sharpens the scope so it is distinguishable from a listing of already-owned numbers. An agent can tell what this returns without opening the schema.

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?

It explicitly places the tool in the acquisition flow ('this follows set_owner_phone, which saves a reachable owner number or records a decline'), giving real ordering context for when to call it. It stops short of naming a when-not-to-use case or an alternative such as list_numbers, so it is clear context without exclusions.

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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