YT-NINJA

download_thumbnail

Download YouTube video thumbnail images by providing a video URL and selecting quality options like maxres, high, medium, or default.

Instructions

Download video thumbnail image

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": {
      "url": "<url>"
    },
    "name": "download_thumbnail"
  }
}

Input Schema

Name	Required	Description
`url`	Yes	YouTube video URL
`outputPath`	No	Output file path (optional)
`quality`	No	Thumbnail quality (default: maxres)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.0Jan 11, 2026

TDQS

C2.9/5.0

Behavior2/5

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. While 'Download' implies file creation, it doesn't specify where files are saved by default, what happens if outputPath isn't provided, whether authentication is needed, or any rate limits. This leaves significant behavioral gaps for a tool that creates files.

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 perfectly concise at just three words, front-loading the essential information with zero wasted words. Every element earns its place in this minimal but complete statement of purpose.

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?

For a tool with 3 parameters, no annotations, and no output schema, the description is insufficiently complete. It doesn't explain what happens when the tool executes (file creation behavior), what format the thumbnail is in, or what happens on errors. The minimal description leaves too many operational questions unanswered.

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?

With 100% schema description coverage, the schema already documents all parameters thoroughly. The description adds no additional parameter semantics beyond what's in the schema, so it meets the baseline but doesn't provide extra value.

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 clearly states the action ('Download') and resource ('video thumbnail image'), making the purpose immediately understandable. However, it doesn't differentiate from sibling tools like 'get_video_info' which might also provide thumbnail data, so it doesn't reach the highest score for sibling differentiation.

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 provides no guidance on when to use this tool versus alternatives. There's no mention of prerequisites, when-not-to-use scenarios, or comparison with sibling tools like 'get_video_info' that might provide thumbnail URLs without downloading files.

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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