list_categoriesRetrieve assignable YouTube video category IDs and names for a region, optionally for a specific connected channel, to select accurate metadata when publishing or updating videos.
YouTube video categories you can assign (id and name) for a region.
| Name | Required | Description | Default |
|---|---|---|---|
| channel | No | Which connected channel: channel ID (UC...), @handle or name. Omit to use the default channel. | |
| region_code | No | US |
Changes observed during successful MCP inspections.
v1.0.1Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered; the description contributes the useful facts that results are region-dependent and consist of id/name pairs. It does not mention that the catalogue comes from YouTube's fixed list, that the connected channel/region determines the result set, or anything about authentication or result size.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.
Is the description appropriately sized, front-loaded, and free of redundancy?
A single short sentence with no filler, and the two most important facts (what it returns, region dependence) are front-loaded. It reads as a fragment rather than a complete statement, which slightly undercuts clarity but wastes nothing.
Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.
Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?
For a simple two-parameter read tool with annotations covering the safety profile, the description conveys returns and region scoping, which is close to sufficient. It stops short of framing the tool's role in the workflow (feeding a category id into video updates) and leaves region_code semantics entirely implicit.
Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.
Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?
Schema coverage is 50% — only 'channel' is documented in the schema, while 'region_code' carries just a default of 'US' and length constraints. The description's phrase 'for a region' does add the crucial meaning that categories vary by region, partially compensating for that gap, but it never explains the format (ISO 3166-1 alpha-2) or what happens when region is omitted.
Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.
Does the description clearly state what the tool does and how it differs from similar tools?
The description identifies the resource clearly ('YouTube video categories') and notes the returned fields (id and name) plus the region scoping, but it is a noun phrase with no explicit verb — the agent must infer that this is a listing/retrieval operation rather than something that creates or validates categories. It is distinguishable from all siblings since none deal with categories, so the gap is phrasing rather than ambiguity.
Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.
Does the description explain when to use this tool, when not to, or what alternatives exist?
There is no explicit when-to-use statement or named alternative, but 'categories you can assign' implicitly signals the workflow: call this to obtain valid category ids before assigning one to a video (e.g., with update_video). Nothing tells the agent when not to call it or whether results are static and cacheable.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.