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

Annotations already provide readOnlyHint=true and destructiveHint=false, covering the safety profile. The description adds valuable behavioral context: it mentions cost ('Spends about a credit'), return format ('compact JSON {desc (title), author, handle, plays, link, cover} per video'), and ordering ('ranked by views'). It also uses 'Organic' to imply non-sponsored results. While it doesn't describe pagination or error cases, the disclosed cost and response structure go beyond what annotations provide, meriting a 4.

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?

The description is two sentences with zero fluff. The core purpose is front-loaded ('Organic YouTube keyword search'), followed by the use case, return format, and cost. Every word earns its place, and the structure makes it easy to scan. It is concise without sacrificing informative detail.

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 2-parameter tool with no output schema, the description is remarkably complete. It covers the purpose, the exact structure of the returned JSON, the ranking criterion, and the cost. An agent can accurately invoke this tool based solely on the description and schema. No critical information is missing for correct usage.

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 description coverage is 100%, with both 'query' and 'limit' documented in the input schema. The description does not add parameter-specific detail beyond the schema, but it does indirectly clarify the query's role by describing the search behavior. Since the schema fully describes the parameters, the baseline of 3 is appropriate; the description adds marginal value but does not need to compensate for gaps.

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 opens with 'Organic YouTube keyword search' which is a specific verb (search) and resource (YouTube), immediately distinguishing it from listing tools like list_youtube_videos. It further specifies the purpose ('videos to mine for hooks/angles/long-form structure'), giving a clear use case. The API endpoint is included, reinforcing what the tool does. This clearly differentiates it from search tools for other platforms (search_instagram, search_tiktok) and internal YouTube management tools.

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?

The description explicitly states the intended use case: 'videos to mine for hooks/angles/long-form structure.' This provides clear context for when to use the tool (content research and ideation). It does not explicitly mention alternatives or when not to use it, but the purpose is so specific that an agent can infer it is the right choice for organic YouTube keyword discovery. It lacks an explicit 'when-not-to-use' or alternative routing, which would earn a 5, but the context is clear enough for a 4.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.