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Change Voice

change_voice

Take a recording of someone speaking and have it said again in a different voice, keeping the original performance exactly: the pauses, the timing, the emphasis and the feeling all stay, only who is speaking changes. Give it source (a recording in your library by id, or an https link to one) and voice (a voice name or a voice id from list_voices). Use "multilingual" (the default) for any language, "english" for an English-only take. Turn remove_background_noise on when the recording has room noise, traffic or hiss behind the speaker. Billed per 10 seconds of audio. This is for re-voicing a real performance; to speak written words from scratch use generate_speech.

Input Schema

NameRequiredDescriptionDefault
modelNoOptional. "multilingual" (default) handles any language; "english" is tuned for English only.
voiceYesThe voice that should say it: a voice name such as "Rachel", or a voice id. Call list_voices to see the voices on this account.
sourceYesThe recording to re-voice: an asset id from the user's library, or an https link to an audio file.
stabilityNoOptional, 0 to 1. Lower keeps more of the original expression, higher steadies the read.
similarityNoOptional, 0 to 1. How closely the result sticks to the new voice.
remove_background_noiseNoOptional. true cleans room noise, traffic or hiss off the recording before the voice is changed.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Added

TDQS

A4.4/5.0
Behavior4/5

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

Annotations already declare it is not read-only, is open-world (https sources), and non-destructive. The description adds billing per 10 seconds and the noise-cleaning behavior expectation, but it still omits whether the result is synchronous or requires polling (e.g., get_audio_status) and what artifact is returned.

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?

Front-loads the core transformation, then moves through required inputs, defaults, optional cleanup, billing, and the alternative tool. Every sentence contributes; no filler.

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?

Covers the required inputs, model default, noise-cleanup guidance, cost, and the key sibling alternative, which is strong for a 6-param tool. However, with no output schema it does not tell the agent what is returned or whether the job is async, a moderate remaining gap.

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 schema already documents all six parameters. The description largely repeats the source/voice/model definitions and the noise flag, adding only a when-to-use cue for remove_background_noise; stability and similarity are left to the schema.

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 transformation—re-voicing a spoken recording while preserving pauses, timing, emphasis and feeling—and names the sibling it is not (generate_speech). An agent can tell exactly what this tool produces and how it differs from text-to-speech.

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

Usage Guidelines5/5

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

Explicitly says to use this for re-voicing a real performance and to use generate_speech for speaking written words from scratch. It also gives when to enable remove_background_noise and how to obtain voice ids from list_voices, leaving little inference.

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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