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YouTube MCP

YouTube MCP

by pratikgh0se
OverviewSchemaSourceRelated ServersDiscussionsAdmin
TypeScript
Local

youtube_preflight_set_thumbnail

Destructive

Validate and preview a thumbnail for an owned YouTube video before setting it, using the video ID, local image path, and JPEG/PNG MIME type.

Instructions

Validate and preview an owned-video thumbnail.

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": {
      "videoId": "<videoId>",
      "filePath": "<filePath>",
      "mimeType": "<mimeType>"
    },
    "name": "youtube_preflight_set_thumbnail"
  }
}

Input Schema

NameRequiredDescriptionDefault
videoIdYesID of an owned video to set the thumbnail on.
filePathYesAbsolute path to the local thumbnail image.
mimeTypeYesThumbnail MIME type: image/jpeg or image/png.

Schema Changelog

Changes observed during successful MCP inspections.

  1. Changed3 schema fields changedv0.3.1
    • addedInput schema / properties / filePath / description
      Added value: +"Absolute path to the local thumbnail image."
    • addedInput schema / properties / mimeType / description
      Added value: +"Thumbnail MIME type: image/jpeg or image/png."
    • addedInput schema / properties / videoId / description
      Added value: +"ID of an owned video to set the thumbnail on."
  2. First observedv0.1.0

TDQS

C2.9/5.0
Behavior2/5

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

The only structured signal is destructiveHint=true, which sits awkwardly beside a description claiming the tool merely 'validates and previews' – the agent cannot tell whether the thumbnail is actually written or not. Nothing is said about which validation rules are applied, whether the upstream API is called, or what a 'preview' consists of.

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?

A single front-loaded sentence with no filler. It is efficient, though the terseness leaves no room for the routing and return-value information this tool needs.

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?

There is no output schema, yet the entire value of a validate-and-preview tool is its result – whether the image passes and what the preview shows. The description says nothing about return shape, and combined with the destructiveHint ambiguity, an agent cannot confidently predict the outcome of a call.

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 videoId, filePath and mimeType are already fully documented including the enum, and the baseline of 3 applies. The description adds no constraints beyond the schema, such as size or dimension limits that thumbnail validation would normally enforce.

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 pair (validate and preview) and a specific resource (an owned-video thumbnail), so an agent knows this is a non-executing inspection step for a thumbnail image. It stops short of distinguishing itself from the sibling youtube_set_thumbnail, which is the obvious next step 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 Guidelines2/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It never states when to use this instead of youtube_set_thumbnail, nor that set_thumbnail should follow a successful preview. The 'preflight' naming convention implies a dry-run, but the description itself offers no when/when-not guidance or prerequisites.

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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