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

Annotations already declare readOnly/idempotent/openWorld/non-destructive, so the description is not carrying the safety burden. It adds real behavioral context beyond them: it runs through the merchant's Google account, is a billed search, is the most expensive YouTube read, and caps results at 50. Return shape is also enumerated, though pagination or rate-limit behavior is not mentioned.

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?

Information is front-loaded with the core purpose in the first sentence, then parameter meanings, then return fields and cost. It is dense but each clause carries a fact; the field enumeration is the only mildly verbose part, though it substitutes for a missing output schema.

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 4-parameter read tool with no output schema and full annotation coverage, the description supplies purpose, parameter formats, returned fields, result cap, and cost implications. It is complete enough to call correctly; only pagination/edge behavior is absent.

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?

With schema description coverage at 0%, the description must compensate and largely does: region is a two-letter country code with examples (TR, US), language is the relevance language with examples (tr, en), and count is bounded ('at most count, up to 50'). Only keyword is left implicit, which is acceptable given the name.

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-equivalent (returns most viewed videos) plus the resource and three scoping axes (keyword, region, language), which lets an agent distinguish it from list_yt_popular or search_tt_videos. It stops short of explicitly naming the sibling it is not, so it is clear but not fully differentiated.

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 or when-not-to-use statement versus siblings like list_yt_popular or search_ig_trends. The only usage signal is implicit: the cost note ('one priced search, the most expensive YouTube read') hints the agent should call it sparingly, which is a useful but partial guideline.

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