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CallMCP — Phone Call MCP Server

by ai.callmcp
OverviewDiscussionsAdmin

List Voice Catalog

list_voices
Read-onlyIdempotent

List the curated, credential-free voice catalog (id, display name, accent, language, gender, sample URL) used to configure agent voices.

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": "list_voices"
  }
}

Input Schema

NameRequiredDescriptionDefault
genderNoFilter by gender: male or female.
languageNoFilter by language label, e.g. English or Spanish.
providerNoFilter by a voice provider id exactly as list_voices returns it.

Output Schema

NameRequiredDescriptionDefault
errorNoPresent when success is false
voicesNo
successYesWhether the tool completed successfully

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changed
    • changedInput schema / properties / provider / description
      Previous value: -"Filter by voice provider id, e.g. 11labs or azure."New value: +"Filter by a voice provider id exactly as list_voices returns it."
  2. First observed

TDQS

A3.7/5.0
Behavior4/5

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuine behavioral context beyond them: the catalog is 'curated' (a fixed, known set) and 'credential-free' (no provider credentials needed to enumerate it), which matters for an agent planning auth and expectations.

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 front-loaded sentence with no filler; the core action comes first. The parenthetical field list is slightly redundant given an output schema exists, but it is compact and readable.

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 no-required-parameter, read-only list tool with full schema coverage and an output schema, the description covers purpose, scope and the nature of the catalog. The only real omission is disambiguation from 'find_voices', which keeps it from a 5.

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 the three filters (gender, language, provider) are already documented, including the 'provider' filter's dependence on ids returned by this same tool. The description adds no filter semantics of its own, so the baseline of 3 applies.

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 ('List the ... voice catalog') and even enumerates the returned fields (id, display name, accent, language, gender, sample URL). It does not differentiate itself from the sibling 'find_voices', so an agent cannot tell from the description alone which of the two to pick.

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 phrase 'used to configure agent voices' implies the downstream purpose, giving an indirect hint about when to reach for it. There is no explicit when-to-use/when-not guidance and no mention of the 'find_voices' alternative despite its presence in the catalog.

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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