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

Annotations already cover readOnly/idempotent/non-destructive, yet the description adds substantive behavior: the candidate universe (1K-1M users, ≥500 net new), the free-tier cap of 10 results on a 30-day window, the caveat that missing comparison data is not zero growth, and that requests never rebuild rankings (staleness/latency signal). These are non-obvious traits an agent could not obtain from annotations or schema.

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 dense sentences, front-loaded with what the tool finds and its thresholds before the free-tier mechanics. Every sentence carries information, though the free-tier and caveat clauses are compressed into near-telegraphic phrasing that takes a re-read.

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 does indicate what comes back (up to 10 extensions ranked by 30-day net user gain) and constrains the candidate set, which is enough to call it correctly. It stops short of naming returned fields or pagination behavior beyond the preview cap.

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 100% and each parameter already documents its const preview value, so the baseline is 3. The description goes further by explaining that the full tool supports 7/14/30/90-day windows and user or rating-count sorts, and that omitting arguments yields the free preview, which gives context for why every parameter is pinned.

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 and resource (find growing extensions) plus the mechanism (saved 7/14/30/90-day user or rating-count growth rankings) and candidate filter (1K-1M users, ≥500 net new users). It never distinguishes itself from close siblings like extension_trends, extension_rankings, extension_top, or extension_rank_history, so an agent cannot route between them from this text alone.

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?

"omit arguments for that preview" gives an operational instruction for the free tier, which is real usage guidance. But there is no statement of when to choose this over extension_trends or extension_rankings, and no explicit when-not-to-use condition, leaving the sibling choice to inference.

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