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runapi-ai

runway-mcp

by runapi-ai
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TypeScript
Remote

extend_video

Extend an existing Runway video task via RunAPI by supplying a source task ID, prompt, and output resolution; returns task ID, status, and output URLs.

Instructions

Create a Runway task on RunAPI (extend video). Returns a task id, status, and output URLs.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
waitNoPoll until the task reaches a terminal status.
modelNoRunAPI model slug for this model line.
promptYesDeclared type: string.
watermarkNoDeclared type: string.
timeout_msNo
callback_urlNoDeclared type: string.
source_task_idYesDeclared type: string.
poll_interval_msNo
output_resolutionYesDeclared type: string. Known values: "720p", "1080p".

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed10 schema fields changedv0.2.0
    • changedInput schema / additionalProperties
      Previous value: -falseNew value: +{}
    • addedInput schema / properties / callback_url / description
      Added value: +"Declared type: string."
    • removedInput schema / properties / model / enum
      Removed value: -[
-  "runway"
-]
    • addedInput schema / properties / output_resolution / description
      Added value: +"Declared type: string. Known values: \"720p\", \"1080p\"."
    • removedInput schema / properties / output_resolution / enum
      Removed value: -[
-  "720p",
-  "1080p"
-]
    • addedInput schema / properties / poll_interval_ms / maximum
      Added value: +9007199254740991
    • addedInput schema / properties / prompt / description
      Added value: +"Declared type: string."
    • addedInput schema / properties / source_task_id / description
      Added value: +"Declared type: string."
    • addedInput schema / properties / timeout_ms / maximum
      Added value: +9007199254740991
    • addedInput schema / properties / watermark / description
      Added value: +"Declared type: string."
  2. Changed5 schema fields changedv0.1.7
    • addedInput schema / properties / callback_url
      Added value: +{
+  "type": "string"
+}
    • addedInput schema / properties / prompt / type
      Added value: +"string"
    • addedInput schema / properties / source_task_id / type
      Added value: +"string"
    • addedInput schema / properties / watermark
      Added value: +{
+  "type": "string"
+}
    • changedInput schema / required
      Previous value: -[
-  "output_resolution"
-]New value: +[
+  "source_task_id",
+  "prompt",
+  "output_resolution"
+]
  3. First observedv0.1.0

TDQS

C2.9/5.0
Behavior2/5

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

No annotations are provided, so the description carries the full behavioral burden. It does disclose the return shape (task id, status, output URLs), which hints at an async task model, but it never states auth requirements, cost implications, or how the wait/poll_interval_ms/timeout_ms/callback_url parameters affect behavior.

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 short, front-loaded sentences with no filler. It is efficient, though arguably so terse that the second sentence is doing all the informational work.

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

Completeness2/5

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

With 9 parameters, no annotations, and no output schema, the description should explain the async polling flow and where source_task_id comes from. It only covers return values, leaving the invocation workflow largely undocumented.

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 78%, close to the high-coverage baseline, so the schema does most of the documenting. The description adds nothing about any of the 9 parameters, leaving the polling and timeout semantics to the schema.

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 concrete verb and resource ('Create a Runway task ... extend video') and names the platform, so the agent knows it initiates a video-extension task. It does not explicitly contrast with the sibling text_to_video, so the differentiation is only implied by the name.

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

Usage Guidelines2/5

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

There is no guidance on when to use this tool versus text_to_video, nor any mention of prerequisites such as needing an existing source_task_id from a prior generation. The agent must infer the workflow entirely.

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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