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video_luma_key

Masks dark regions in a video using a luminance threshold, making pixels below the threshold transparent and saving the keyed output.

Instructions

Mask out dark regions based on luminance (brightness).

Args: input_path: Absolute path to the input video. threshold: Luminance threshold (0.0-1.0). Pixels darker than this become transparent. output_path: Where to save the output. Auto-generated if omitted.

Input Schema

NameRequiredDescriptionDefault
overwriteNoExplicitly allow replacing existing media. Existing non-media files are protected.
thresholdNo
input_pathYes
output_pathNo

Output Schema

NameRequiredDescriptionDefault

No arguments

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed1 schema field changedv1.16.4
    • addedInput schema / properties / overwrite
      Added value: +{
+  "default": false,
+  "description": "Explicitly allow replacing existing media. Existing non-media files are protected.",
+  "title": "Overwrite",
+  "type": "boolean"
+}
  2. Changed1 schema field changedv1.16.0
    • addedInput schema / additionalProperties
      Added value: +false
  3. Addedv1.5.1

TDQS

B3.3/5.0
Behavior3/5

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

With no annotations, the description carries the full burden and does disclose the key behavior: pixels darker than the threshold become transparent, and output_path is auto-generated if omitted. However, it does not state that this is a write operation or explain overwrite safety beyond what the schema provides.

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?

The description is short and front-loaded, leading with the core operation before listing args. The argument list is efficient and each sentence contributes useful information.

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?

The tool is conceptually simple and output schema exists, but with no annotations the description should do more to signal that it is a mutating operation and to differentiate it from other masking tools. It is adequate for calling the tool but incomplete for selection guidance.

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

Parameters4/5

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

Schema description coverage is only 25%, so description must compensate. It documents three of four parameters: input_path as an absolute path, threshold as a 0.0–1.0 luminance cutoff whose effect is explained, and output_path as auto-generated when omitted; overwrite is left to the schema description.

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 states a specific verb and resource: "Mask out dark regions based on luminance (brightness)." This clearly distinguishes a luma key operation from a chroma key, but it does not explicitly name the sibling alternatives such as video_chroma_key or video_shape_mask.

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?

The description gives no guidance on when to use this tool versus alternatives like video_chroma_key, video_shape_mask, or video_filter. It only documents arguments, leaving the agent to infer the selection context.

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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