justcaptions

run_demo

Export the bundled 6-second human-narration sample with animated captions to test styles locally without API keys, uploads, or model downloads.

Instructions

Export the bundled 6-second human-narration sample with animated captions. No API key, upload or model download required. Credits are bundled with the sample.

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": {
      "output_dir": "<output_dir>"
    },
    "name": "run_demo"
  }
}

Input Schema

Name	Required	Description	Default
`style_id`	No		word-highlight
`output_dir`	Yes

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.4.0Oct 7, 2026

TDQS

B3.2/5.0

Behavior3/5

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

Annotations mark it non-read-only, non-idempotent and non-destructive, so the safety profile is partly covered. The description adds genuinely useful behavioral context not in the annotations - that no API key is needed and credits are bundled (cost implications). It does not disclose where the file lands or what happens on repeated runs.

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?

Three short, front-loaded sentences with no filler - the core action leads and the setup/cost caveats follow. Appropriately sized for a simple demo tool.

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

Completeness3/5

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

An output schema exists, so return values need not be explained, and the tool's purpose and prerequisites are clear. Still, the two parameters - notably style_id's semantics and output_dir's role - remain unexplained, which is a real gap for a tool that writes a file somewhere.

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

Parameters2/5

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

Schema description coverage is 0%: neither style_id (with default 'word-highlight') nor the required output_dir is documented anywhere, and the description never mentions them. It therefore fails to compensate for the schema gap, leaving both parameters opaque.

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 (Export) and resource (bundled 6-second human-narration sample with animated captions), and the 'bundled sample / no upload' framing implicitly distinguishes it from caption_video, which processes user footage. It does not explicitly name that sibling, so differentiation is inferred rather than stated.

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?

The 'no API key, upload or model download required' and 'credits bundled' lines imply a zero-setup trial/evaluation use case, which is useful context. However, there is no explicit statement of when to prefer this over caption_video or when it is inappropriate, leaving routing to inference.

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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