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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered structurally. The description does add non-obvious behavior — per-row billing with `limit` capping both rows and cost, and a note that results are user-generated content to treat as untrusted — but it stops short of describing pagination or how the row ranking is computed.

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?

Front-loaded with the core action and sort dimensions, then filters, then routing, then billing/safety. The middle filter enumeration sentence is dense and duplicates schema detail, costing a little efficiency.

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 14-parameter, high-coverage-schema listing tool with no output schema, the description covers ranking defaults, filtering scope, sibling routing, cost model and untrusted-input caution. Nothing material an agent needs to invoke it correctly 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 already 93%, so the baseline is 3, but the description adds genuine meaning beyond the schema: it summarizes the filter set, states that default ranking is by followers, and clarifies that `limit` governs both result size and cost.

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 ('Rank Instagram accounts by followers, media_count or following') and immediately names the scope of its filters. It also distinguishes itself from two siblings (search_users, search_users_by_demographics) without requiring the reader to open 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?

Gives an explicit routing rule: use this when face-detection filters are NOT needed, and use `search_users_by_demographics` when they are, with the reason (this scans all accounts, not only face-detected ones). That is a real when/when-not decision an agent can act on.

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