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

Annotations already declare readOnlyHint=false, destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the safety profile is covered. The description meaningfully extends that by disclosing the billing model (one monthly-quota request per successful call, failures uncharged) and the cache semantics, which the annotations do not convey. It does not contradict the destructiveHint annotation — the quota spend is an observable side effect consistent with a non-read-only classification.

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?

Three dense sentences with zero filler: results scope first, then the cost warning most likely to change agent behavior, then the endpoint. Every clause earns its place and the constraint is front-loaded.

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 7-parameter, quota-metered search with no output schema, the description covers what is returned at a high level (videos, channels, ads), the cost, and the endpoint. Return-shape detail is partially covered by the params' description of top-level keys, but the description itself stops short of describing the response structure an agent would need to consume it.

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 every parameter (q, gl, hl, sp, cache, fields, location) is already documented in the schema, including cross-references to zenserp_list_countries/languages and locations. The description only adds 'optionally by location', which is redundant with the schema. Baseline 3 applies.

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 resource (YouTube search results: videos, channels, ads) with an optional location qualifier and pins it to the concrete endpoint GET /v2/search with search_engine=youtube.com. It does not explicitly contrast with the sibling zenserp_video_search, so an agent must infer the boundary, but the scope is otherwise unambiguous.

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 gives one operational guideline — 'do not repeat a call needlessly' — tied to the quota cost, which is genuinely useful. However, it offers no guidance on when to pick this over zenserp_video_search, zenserp_search, or the other media search siblings, so the alternative-selection decision is left implicit.

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