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ff-toolkit

ff-toolkit

by inthepond
OverviewSchemaSourceRelated ServersDiscussionsAdmin
Python
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ffkit_add_subtitles

Adds subtitles to a video file. Choose 'burn' to hard-code subtitles into the video pixels or 'embed' to keep them as a selectable soft subtitle track.

Instructions

Add subtitles to a video. 'burn' hard-codes into pixels; 'embed' adds as a soft subtitle track.

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_path": "<output_path>",
      "subtitle_path": "<subtitle_path>"
    },
    "name": "ffkit_add_subtitles"
  }
}

Input Schema

NameRequiredDescriptionDefault
modeNoSubtitle mode. Default: burn.
input_pathYesSource video file.
output_pathYesOutput video file.
subtitle_pathYesPath to subtitle file (.srt, .ass, .vtt).

Schema Changelog

Changes observed during successful MCP inspections.

  1. First observedv0.1.0

TDQS

A4.3/5.0
Behavior4/5

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

With no annotations provided, the description carries the full burden of behavioral disclosure. It effectively describes the two behavioral modes, clarifying that 'burn' permanently alters pixels. For a non-destructive operation like 'embed', no further behavioral caveats are needed, but some details about encoding support could improve transparency.

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?

The description is a single, well-structured sentence—front-loaded with the purpose, followed by clarification of the key parameter. Every word adds value with no redundancy or fluff.

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 4-parameter tool with 100% schema coverage, 3 required parameters, and no output schema, the description is complete. It explains the purpose, the critical mode parameter, and the supported subtitle formats. No further information about return values is needed since there is no output schema, and the tool's effect is straightforward.

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 100%, so each parameter (input_path, output_path, subtitle_path, mode) already has a description. The description adds value by explaining the enum values 'burn' and 'embed' more concretely, but does not provide extra semantics for the path parameters beyond what the schema already defines.

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 clearly states the verb 'add' and the resource 'subtitles to a video'. It distinguishes between the two modes 'burn' and 'embed', explaining their effects. This helps differentiate from sibling tools like ffkit_clip, ffkit_extract_audio, ffkit_merge, and ffkit_transcode.

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?

The description implicitly guides usage by explaining when to use 'burn' (hard-coding into pixels) vs 'embed' (soft subtitle track). This helps the agent choose the appropriate mode, but does not explicitly state when not to use this tool or suggest 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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