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

Annotations already cover the safety profile (readOnlyHint=true, destructiveHint=false, openWorldHint=true), and the description adds genuinely useful non-annotation context: billing at $0.005 per page and the fields returned. It does not discuss rate limits, pagination cost scaling (pages 1-20), or error behavior, keeping it short of a 5.

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?

Four short sentences, front-loaded with the purpose and followed by return fields, the alternative routing, and pricing. Dense but no filler; the return-field list is the only slightly expendable part since no output schema exists and it serves completeness.

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?

With no output schema, the description compensates by enumerating return fields, and it discloses the per-page cost, which matters for the pages parameter. It leaves the sentiment surcharge and pagination behavior to the schema, but nothing critical to calling the tool is missing.

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%, so query, pages, upload_date and get_sentiment are already documented with enums and defaults. The description only restates the keyword and upload-date filter, adding no syntax or format detail beyond the schema, which is the expected baseline.

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?

States a specific verb (search) and resource (YouTube videos) plus the matching mechanism (by keyword), and explicitly names the sibling youtube_video_details for the single-video case. An agent can distinguish it from search_youtube_channels and youtube_video_details without opening any schema.

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?

"Use youtube_video_details for one video's full metadata" gives an explicit alternative and the condition that selects it. It does not state when-not to search at all (e.g. broad vs. narrow queries) or mention sibling search_youtube_channels, so it stops short of full routing guidance.

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