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

Goes well beyond the annotations (which only cover read-only/idempotent safety) by disclosing the hard 100-id cap with silent server-side dropping of extras, the absence of error rows for missing ids, non-guaranteed row ordering, per-returned-row billing, and that returned content is untrusted user-generated input. These are exactly the operational traits an agent cannot infer from structured fields.

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 purpose and the alternative it replaces, then packed with behavioral facts; nearly every clause carries unique information. It is dense rather than padded, though the long single-block run of caveats could be split for scanability.

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 compensates by enumerating the returned row fields (pk, username, is_verified, follower_count, biography length, etc.) and by covering edge cases: missing ids, ordering, cap, and billing. Nothing needed to call this 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 100%, so the baseline is 3 and the schema already explains that pk strings avoid JS safe-integer overflow and that extras are dropped. The description adds genuine meaning beyond the schema by noting that `limit` caps both rows and cost, tying a parameter to billing behavior.

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 ('Get ... Instagram user profiles by pk') and adds the batch scope ('up to 100 ... in a single call') that separates it from the singular sibling get_user_by_id. An agent can route between the batch and single-id tools without opening either 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?

Explicitly instructs 'use it instead of repeated `get_user_by_id` calls,' naming the alternative and the condition that selects it. The implied complement (a single id goes to the singular tool) is directly supported by the named sibling.

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