Kuro

Extract a video frame

extract_video_frame

Save the first or last decoded frame of an owned video as a new image generation. Costs no credits; uses account storage. get_generation waits for the result. To go longer than one clip, carry the last frame into the next generate_clip, then join_clips. Not for speech: each line of a talking head starts from the same portrait, because chaining frames drifts the face.

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": "extract_video_frame"
  }
}

Input Schema

Name	Required	Description	Default
`source`	Yes
`position`	No		first

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

A4.4/5.0

Behavior4/5

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

Beyond the annotations it discloses two behaviors an agent could not infer: the call costs no credits but consumes account storage, and get_generation is the way to wait for the result. With readOnlyHint=false and destructiveHint=false already declared, this is strong added context, though it does not say what happens if the source video is not owned or still processing.

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 dense sentences with the core action first, followed by cost, polling, and chaining guidance. The closing speech caveat is niche but earns its place by preventing a costly misuse; there is no filler.

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?

For a two-parameter tool with an output schema and full annotations, the description covers action, cost, storage side effect, result retrieval, and chaining workflow. Nothing essential to correct invocation 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 0%, so the description must carry parameter meaning. It conveys the position semantics ('first or last decoded frame', matching the first/last enum) and implies source is an owned video, but it never clarifies that source is a discriminated union of an upload_id or generation_id, so half the parameter shape stays undocumented.

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 names a specific verb and resource — saving the first or last decoded frame of an owned video as a new image generation — which is unambiguous and clearly distinct from siblings like trim_video, join_clips, or generate_image.

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?

It explicitly states the downstream pattern (carry the last frame into generate_clip, then join_clips to go beyond one clip) and an explicit when-not-to-use case (talking-head speech, because chaining frames drifts the face), naming the reason rather than just the rule.

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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