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text_to_speech_synthesize

Read-onlyIdempotent

Text to Speech: speak text with one of four voices and get the audio back as base64 (MP3 by default, or WAV) with its length in seconds. Counts as 25 calls against the plan allowance. A trial key gets 20 synthesize calls in total and up to 500 characters each; paid plans allow up to 2,000 characters. Busy servers answer 429 with a retry time. Nothing is stored.

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": {
      "text": "<text>"
    },
    "name": "text_to_speech_synthesize"
  }
}

Input Schema

Name	Required	Description
`text`	Yes	The text to speak: up to 500 characters on a trial key, 2,000 on a paid plan.
`speed`	No	Speaking speed from 0.5 to 2. Default 1.
`voice`	No	Default amy. amy, lessac and ryan are American English; alba is British (Scottish).
`format`	No	Default mp3.
`delivery`	No	natural (default) varies pace and adds pauses between sentences; plain speaks it flat.

Schema Changelog

Changes observed during successful MCP inspections.

AddedNov 10, 2026

TDQS

A4.1/5.0

Behavior4/5

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

Beyond the annotations (readOnly, idempotent, non-destructive, closed-world), the description adds genuinely useful behavior: it costs 25 calls against the plan allowance, trial keys get only 20 total calls, busy servers return 429 with a retry time, and nothing is stored. The omissions are minor – no pagination/streaming detail, but audio-return tools rarely need it.

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?

Five short sentences, front-loaded with purpose and return format, then cost, quota, error and privacy in descending order of importance. Nothing is padded or repeated; every clause carries a distinct fact.

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

Completeness5/5

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

There is no output schema, so the description must describe the return value, and it does (base64 audio, MP3/WAV, length in seconds). With all five parameters fully covered by the schema, the description only needs the operational context it supplies – billing cost, quota caps, rate-limit behavior, statelessness.

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 enum values, speed range and default voice are already documented. The description only duplicates the payload limits (500/2,000 characters) and the count of voices, adding no syntax or format detail the schema lacks, 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 opens with a specific verb and resource ("speak text") and states the return shape precisely: base64 audio, MP3 default or WAV, plus its length in seconds. That output-level detail distinguishes it from the sibling voice-listing tool without needing to name it.

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?

Usage conditions are implied through constraints (trial key limits, per-plan character caps, 429 behavior) rather than explicit when-to-use or when-not-to-use guidance against alternatives. An agent can infer it is the synthesis endpoint, but no alternative is named or excluded.

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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