Kuro

Loop a performance bank

loop_video

Rotate one to three owned 1–15 second video takes to a target duration, up to 30 minutes. Plain loop or ping-pong. Output is silent for dubbing. Free; uses storage. 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": {
      "sources": "<sources>",
      "duration_seconds": "<duration_seconds>"
    },
    "name": "loop_video"
  }
}

Input Schema

Name	Required	Default
`mode`	No	loop
`sources`	Yes
`duration_seconds`	Yes

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

A4.1/5.0

Behavior4/5

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

Annotations only declare the generic mutation profile (not read-only, not destructive, not idempotent); the description adds substance beyond that — output is silent for dubbing, cost is free but storage is consumed, and the call is asynchronous with get_generation as the completion path. It does not say what artifact is created or whether a prior generation must be complete before it can be used as a source.

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 clauses, each carrying distinct information (scope, mode, output property, cost, async follow-up), with the core action front-loaded. Nothing is redundant or padded.

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 three-parameter mutation with nested source variants and an output schema, the description covers the essentials an agent needs — input limits, mode choice, output nature, cost, and polling. It leaves minor gaps around failure behavior and source-precondition requirements, but the output schema already handles return-value questions.

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 coverage is 0%, so the description must carry the burden and largely does: 'sources' is characterized as one to three owned 1–15 second takes (implying upload or generation references), 'duration_seconds' is bounded at 30 minutes matching the 1800 maximum, and 'mode' is explained as 'plain loop or ping-pong'. The upload_id vs generation_id discrimination is left only 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?

The description gives a specific verb and resource ('Rotate one to three owned 1–15 second video takes to a target duration') plus hard constraints (1–3 sources, 1–15s inputs, 30-minute cap), which clearly separates it from trim_video or join_clips. It never names an alternative sibling, so the agent must infer the routing rather than being told it.

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

Usage Guidelines4/5

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

It gives real operational context: the job is free but consumes storage, and the result must be fetched via get_generation, which tells the agent the call is asynchronous. It stops short of stating when to prefer this over trimming or joining clips, or what happens if a source exceeds the 15-second limit.

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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