Kuro

Change a video's voice

change_video_voice

Replace the speech voice in an owned clip with an ElevenLabs voice, saving a new generation using account entitlements. Pass exactly one of voice_id or subject (a Subject with an ElevenLabs voice). get_generation waits for the result.

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": {
      "source": "<source>"
    },
    "name": "change_video_voice"
  }
}

Input Schema

Name	Required	Description
`source`	Yes
`subject`	No	A Subject's name or id with a bound ElevenLabs voice.
`voice_id`	No

Output Schema

Name	Required	Description	Default
`message`	Yes
`generation`	Yes	One image, clip, voice-over or piece of music.

Schema Changelog

Changes observed during successful MCP inspections.

Changed20 schema fields changedNov 4, 2026

addedOutput schema / properties / generation / description

Added value: +"One image, clip, voice-over or piece of music."

addedOutput schema / properties / generation / properties / app_url / description
```
Added value: +"Opens it in the app."
```
addedOutput schema / properties / generation / properties / aspect_ratio / description
```
Added value: +"Null for audio."
```
addedOutput schema / properties / generation / properties / created_at / format
```
Added value: +"date-time"
```

addedOutput schema / properties / generation / properties / credits

Added value: +{
+  "description": "Credits charged. Zero when your own provider key or the free allowance paid.",
+  "type": [
+    "number",
+    "null"
+  ]
+}

removedOutput schema / properties / generation / properties / credits_cost
```
Removed value: -{
-  "type": [
-    "number",
-    "null"
-  ]
-}
```
addedOutput schema / properties / generation / properties / error / description
```
Added value: +"Why it failed. Null otherwise."
```
removedOutput schema / properties / generation / properties / generation_id
```
Removed value: -{
-  "format": "uuid",
-  "type": "string"
-}
```

addedOutput schema / properties / generation / properties / id

Added value: +{
+  "format": "uuid",
+  "type": "string"
+}

removedOutput schema / properties / generation / properties / kind

Removed value: -{
-  "enum": [
-    "image",
-    "video",
-    "audio",
-    "tool"
-  ],
-  "type": "string"
-}

addedOutput schema / properties / generation / properties / model / description
```
Added value: +"The model id it was made with (`GET /v1/models`)."
```

addedOutput schema / properties / generation / properties / object

Added value: +{
+  "const": "generation",
+  "type": "string"
+}

addedOutput schema / properties / generation / properties / output_url / description

Added value: +"The finished file, once `ready`. A signed link that works for about an hour; read the generation again for a fresh one."

addedOutput schema / properties / generation / properties / paid_by / description

Added value: +"Who paid: \"credits\", \"house\" (the free allowance), \"server\" (a server that charges nothing), or the vendor of your own key (\"replicate\", \"fal\", …)."

addedOutput schema / properties / generation / properties / ready_in_seconds / description

Added value: +"Roughly how long an unfinished generation has left; 0 means past its usual time."

addedOutput schema / properties / generation / properties / recipe_id

Added value: +{
+  "anyOf": [
+    {
+      "$ref": "#/properties/generation/properties/id"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "description": "The recipe it was made with, if any."
+}

addedOutput schema / properties / generation / properties / status / description
```
Added value: +"`ready` and `failed` are final."
```

addedOutput schema / properties / generation / properties / thumbnail_url

Added value: +{
+  "anyOf": [
+    {
+      "$ref": "#/properties/generation/properties/output_url/anyOf/0"
+    },
+    {
+      "type": "null"
+    }
+  ],
+  "description": "A small still of the result, for a grid. Null for audio and while it works."
+}

addedOutput schema / properties / generation / properties / type

Added value: +{
+  "description": "What was made. New values may be added; treat an unknown one as opaque.",
+  "enum": [
+    "image",
+    "clip",
+    "voiceover",
+    "music",
+    "tool"
+  ],
+  "type": "string"
+}

changedOutput schema / properties / generation / required

Previous value: -[
-  "generation_id",
-  "kind",
-  "status",
-  "model",
-  "prompt",
-  "aspect_ratio",
-  "refined_from",
-  "caption_style",
-  "output_url",
-  "credits_cost",
-  "paid_by",
-  "error",
-  "vendor_phase",
-  "stalled",
-  "ready_in_seconds",
-  "created_at",
-  "app_url"
-]New value: +[
+  "object",
+  "id",
+  "type",
+  "status",
+  "model",
+  "prompt",
+  "aspect_ratio",
+  "output_url",
+  "thumbnail_url",
+  "credits",
+  "paid_by",
+  "error",
+  "ready_in_seconds",
+  "recipe_id",
+  "created_at",
+  "app_url",
+  "refined_from",
+  "caption_style",
+  "vendor_phase",
+  "stalled"
+]

Changed2 schema fields changedOct 26, 2026

addedOutput schema / properties / generation / properties / paid_by
```
Added value: +{
+  "type": [
+    "string",
+    "null"
+  ]
+}
```

changedOutput schema / properties / generation / required

Previous value: -[
-  "generation_id",
-  "kind",
-  "status",
-  "model",
-  "prompt",
-  "aspect_ratio",
-  "refined_from",
-  "caption_style",
-  "output_url",
-  "credits_cost",
-  "error",
-  "vendor_phase",
-  "stalled",
-  "ready_in_seconds",
-  "created_at",
-  "app_url"
-]New value: +[
+  "generation_id",
+  "kind",
+  "status",
+  "model",
+  "prompt",
+  "aspect_ratio",
+  "refined_from",
+  "caption_style",
+  "output_url",
+  "credits_cost",
+  "paid_by",
+  "error",
+  "vendor_phase",
+  "stalled",
+  "ready_in_seconds",
+  "created_at",
+  "app_url"
+]

Changed2 schema fields changedOct 21, 2026

addedOutput schema / properties / generation / properties / ready_in_seconds
```
Added value: +{
+  "type": [
+    "number",
+    "null"
+  ]
+}
```

changedOutput schema / properties / generation / required

Previous value: -[
-  "generation_id",
-  "kind",
-  "status",
-  "model",
-  "prompt",
-  "aspect_ratio",
-  "refined_from",
-  "caption_style",
-  "output_url",
-  "credits_cost",
-  "error",
-  "vendor_phase",
-  "stalled",
-  "created_at",
-  "app_url"
-]New value: +[
+  "generation_id",
+  "kind",
+  "status",
+  "model",
+  "prompt",
+  "aspect_ratio",
+  "refined_from",
+  "caption_style",
+  "output_url",
+  "credits_cost",
+  "error",
+  "vendor_phase",
+  "stalled",
+  "ready_in_seconds",
+  "created_at",
+  "app_url"
+]

First observedOct 15, 2026

TDQS

A3.8/5.0

Behavior4/5

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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent, closed-world operation, so the bar is lowered. The description still adds genuinely useful context beyond them: the result is a *new* generation (the source is not mutated), it consumes account entitlements/credits via ElevenLabs, and the caller should follow up with get_generation for completion. It stops short of explaining what happens to background audio/music or the failure mode when entitlements are exhausted.

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?

Two sentences, no filler, with the operation and its effect front-loaded and the parameter constraint plus follow-up tool packed at the end. "using account entitlements" is slightly opaque phrasing that could be sharpened to name credit consumption, but nothing is redundant.

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 an output schema present, return values need no prose, and the async hand-off to get_generation is covered; the credit/entitlement requirement for an annotation-light mutation tool is also disclosed. The remaining gap is the side effects on non-speech audio and whether the source clip stays untouched, which matter for a transformation tool but are only partially implied by "saving a new generation."

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 33%, so the description must compensate and largely does: it introduces a mutual-exclusion rule between voice_id and subject that appears nowhere in the schema, and clarifies that subject means a Subject with a bound ElevenLabs voice. The source parameter is only indirectly covered via "owned clip," leaving the upload vs. generation variant choice to the schema's anyOf.

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?

"Replace the speech voice in an owned clip with an ElevenLabs voice, saving a new generation" states a specific verb (replace voice), resource (owned clip), and output (new generation). It is clear on its own, but it never names or contrasts with nearby siblings such as cast_voice, generate_voiceover, or save_voice, so an agent must infer the boundary itself.

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?

"Pass exactly one of voice_id or subject" gives a real usage constraint and "get_generation waits for the result" hands off the polling step correctly. However, there is no statement of when to prefer this over cast_voice or generate_voiceover, nor any precondition beyond "owned" — the selection guidance is implied rather than spelled out.

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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