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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-obvious behavior: the cost (1 credit), the ranking provenance (YouTube's hashtag landing page order), and the important caveat that `type=shorts` returns a distinct result set rather than a filtered subset.

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, each carrying distinct information, front-loaded with purpose before the param caveat and the cost note. Nothing is redundant.

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 adequately characterizes the return as ranked hashtag-landing-page results, and it discloses the credit cost. Minor gaps are the unstated meaning of `cache_max_age` and how pagination continues, both partly covered by the cursor schema field.

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 only 50%, but the description compensates for the most consequential gap by explaining the `type` enum's behavior beyond its default value. The hashtag and cursor params are already covered in the schema; only `cache_max_age` remains undocumented in both places.

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 gives a specific verb and resource ('Search by hashtag') and further pins down the result set as videos/Shorts carrying the tag, ranked as on YouTube's hashtag landing page. It is clearly distinct from a general keyword search, though it never names youtube_search as the sibling alternative.

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?

It explains the key decision point for `type`: `shorts` switches to a different result set rather than filtering, which guides correct selection between the two modes. However, it gives no guidance on when to prefer this tool over youtube_search or youtube_searchTypeahead, and no stated preconditions.

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