justcaptions

caption_video

Start captioning local videos or folders with animated captions, then poll the returned job ID for completion.

Instructions

Start captioning one local video or a folder. Returns a job ID immediately; poll get_job. API recognition sends audio, AI edits send text, and MP4 rendering remains local. captions_path reuses an existing SRT/VTT/JSON without recognition. Original video is preserved.

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": {
      "input_path": "<input_path>",
      "output_dir": "<output_dir>"
    },
    "name": "caption_video"
  }
}

Input Schema

Name	Required	Default
`burn`	No
`size`	No	medium
`engine`	No	auto
`length`	No	medium
`correct`	No
`glossary`	No
`language`	No
`position`	No	bottom
`style_id`	No	word-highlight
`overrides`	No
`overwrite`	No
`safe_area`	No	tiktok
`input_path`	Yes
`output_dir`	Yes
`translate_to`	No
`captions_path`	No

Output Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.4.0Oct 7, 2026

TDQS

A4.1/5.0

Behavior5/5

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

Adds substantial behavior beyond the annotations: the call is asynchronous and returns a job ID, audio is transmitted off-machine for API recognition, AI edits send text, MP4 rendering stays local, and the original video is preserved. The privacy/processing split and the non-destructive guarantee are exactly the context an agent needs before invoking.

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 short, dense sentences with the core action and polling contract front-loaded; nothing is padding. Slightly telegraphic phrasing ("API recognition sends audio") costs a little readability but wastes no space.

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 no explanation, and the async flow plus preservation guarantee cover the biggest risks. For a 16-parameter tool, though, the silence on rendering/style/translation options and on overwrite versus preserve behavior leaves real gaps.

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% across 16 parameters, so the description must carry the load, and it explains only two: captions_path's bypass behavior and the implicit engine split (api vs local). The remaining 14 parameters (burn, size, length, correct, glossary, language, position, style_id, overrides, overwrite, safe_area, translate_to, input_path, output_dir) get no semantics at all.

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?

Opens with a specific verb+resource ("Start captioning one local video or a folder") and immediately clarifies the async contract ("Returns a job ID immediately; poll get_job"). No sibling tool does captioning, and it names get_job as the poll target, so an agent can place it precisely in the workflow.

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?

Gives clear operational context: start the job here, then poll get_job; and states the alternate entry path ("captions_path reuses an existing SRT/VTT/JSON without recognition") that skips recognition. It does not state when not to use it or contrast engine choices as a decision rule, so it falls short of explicit alternatives.

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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