SoapBox Faith

synthesize_speech

Idempotent

Generate spoken-audio (text-to-speech) for a verse, prayer, or devotional in 50+ languages, and get back a playable audio URL. Pass a BCP-47 language (e.g. en-US, es-ES, sw-KE, fil-PH, cmn-CN), optional voice/gender. Results are cached. Requires an API key (audio generation has real cost).

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": "synthesize_speech"
  }
}

Input Schema

Name	Required	Description	Default
`text`	Yes	The text to synthesize into speech (a verse, prayer, or short devotional).
`voice`	No	Optional specific Google Cloud TTS voice name; overrides the default voice for the language. Pass the matching language with it.
`format`	No	Audio container/encoding of the returned URL.	mp3
`gender`	No	Preferred voice gender when a specific voice is not named.	NEUTRAL
`language`	No	BCP-47 language tag for the voice, as Google Cloud TTS names it: en-US, es-ES, sw-KE, fil-PH (Tagalog/Filipino), cmn-CN (Mandarin). 'tl' is accepted for fil-PH and 'zh' for cmn-CN. If omitted and a voice is named, the voice's own locale is used.	en-US

Schema Changelog

Changes observed during successful MCP inspections.

Changed6 schema fields changedOct 25, 2026

changedInput schema / properties / language / description

Previous value: -"BCP-47 language tag for the voice."New value: +"BCP-47 language tag for the voice, as Google Cloud TTS names it: en-US, es-ES, sw-KE, fil-PH (Tagalog/Filipino), cmn-CN (Mandarin). 'tl' is accepted for fil-PH and 'zh' for cmn-CN. If omitted and a voice is named, the voice's own locale is used."

changedInput schema / properties / language / examples

Previous value: -[
-  "en-US",
-  "es-ES",
-  "sw-KE"
-]New value: +[
+  "en-US",
+  "es-ES",
+  "sw-KE",
+  "fil-PH",
+  "cmn-CN"
+]

addedInput schema / properties / language / maxLength
```
Added value: +35
```

changedInput schema / properties / language / pattern

Previous value: -"^[a-z]{2}-[A-Z]{2}$"New value: +"^[A-Za-z]{2,3}(-[A-Za-z0-9]{1,8})*$"

changedInput schema / properties / voice / description

Previous value: -"Optional specific Google Cloud TTS voice name; overrides the default voice for the language."New value: +"Optional specific Google Cloud TTS voice name; overrides the default voice for the language. Pass the matching language with it."

changedInput schema / properties / voice / examples

Previous value: -[
-  "en-US-Neural2-D"
-]New value: +[
+  "en-US-Neural2-D",
+  "fil-PH-Chirp3-HD-Achernar",
+  "cmn-CN-Chirp3-HD-Achernar"
+]

Changed16 schema fields changedJul 20, 2026

addedInput schema / properties / format / default
```
Added value: +"mp3"
```

changedInput schema / properties / format / description

Previous value: -"mp3 (default) or ogg."New value: +"Audio container/encoding of the returned URL."

addedInput schema / properties / format / enum
```
Added value: +[
+  "mp3",
+  "ogg"
+]
```
addedInput schema / properties / gender / default
```
Added value: +"NEUTRAL"
```

changedInput schema / properties / gender / description

Previous value: -"NEUTRAL | MALE | FEMALE (default NEUTRAL)."New value: +"Preferred voice gender when a specific voice is not named."

addedInput schema / properties / gender / enum

Added value: +[
+  "NEUTRAL",
+  "MALE",
+  "FEMALE"
+]

addedInput schema / properties / language / default
```
Added value: +"en-US"
```

changedInput schema / properties / language / description

Previous value: -"BCP-47 language code, e.g. en-US, es-ES, sw-KE (default en-US)."New value: +"BCP-47 language tag for the voice."

addedInput schema / properties / language / examples

Added value: +[
+  "en-US",
+  "es-ES",
+  "sw-KE"
+]

addedInput schema / properties / language / pattern
```
Added value: +"^[a-z]{2}-[A-Z]{2}$"
```

changedInput schema / properties / text / description

Previous value: -"Text to speak (max 2000 chars)."New value: +"The text to synthesize into speech (a verse, prayer, or short devotional)."

addedInput schema / properties / text / examples

Added value: +[
+  "For God so loved the world..."
+]

addedInput schema / properties / text / maxLength
```
Added value: +2000
```
addedInput schema / properties / text / minLength
```
Added value: +1
```

changedInput schema / properties / voice / description

Previous value: -"Optional specific Google voice name."New value: +"Optional specific Google Cloud TTS voice name; overrides the default voice for the language."

addedInput schema / properties / voice / examples
```
Added value: +[
+  "en-US-Neural2-D"
+]
```

First observedJun 14, 2026

TDQS

A3.7/5.0

Behavior4/5

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

Annotations already declare idempotent, non-destructive and non-read-only, and the description adds value beyond them: results are cached (consistent with idempotentHint), an API key is required, and generation has real cost. It doesn't state rate limits or failure behaviour, which keeps it 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?

Four tight sentences, front-loaded with purpose and return value, followed by input conventions and then the cost/auth caveat. Every sentence carries information, though the language-tag examples duplicate the schema.

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?

With no output schema, the description correctly states what comes back (a playable audio URL). Combined with caching, auth and cost disclosures plus a fully documented 5-parameter schema, an agent has enough to call it correctly; only the relationship to get_audio_devotional is missing.

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 the baseline is 3. The description repeats language examples and the voice-overrides-language rule that the schema already documents, adding essentially no semantics the schema lacks.

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 ('Generate spoken-audio (text-to-speech)'), its scope (verse, prayer, devotional, 50+ languages) and its return value (a playable audio URL). It does not differentiate itself from the sibling get_audio_devotional, which appears to overlap in purpose, so it falls short of a 5.

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 is implied rather than stated: pass text plus a BCP-47 language, optionally a voice or gender. There is no explicit 'use this when...' guidance and no mention of when get_audio_devotional would be the better choice, leaving the agent to infer the boundary from the sibling's name.

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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