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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, non-destructive), and the description adds substantial non-obvious context: billing is per returned row, limit caps both rows and cost, and the content is user-generated and should be treated as untrusted input. The untrusted-input warning and cost model are exactly the kind of disclosure annotations cannot provide.

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 what the tool does and how it matches before moving to alternatives, return fields, and billing. No sentence is filler; each one covers routing, payload, cost, or safety.

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?

There is no output schema, and the description compensates by enumerating the returned fields (pk, code, taken_at, media_type, like_count, comment_count) and pointing to get_media_by_code for the caption text. Combined with the cost and trust guidance, an agent has everything needed to call and consume this tool correctly.

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%, so the baseline is 3, but the description adds meaning beyond the schema: it clarifies that query is a case-insensitive substring match and that limit caps both row count and billed cost, which is a semantic the schema's '1-100' range does not convey.

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 (search) and resource (Instagram post captions) with the matching rule (case-insensitive substring) and ordering (most-liked first). An agent can distinguish it from get_users_by_hashtag, search_comments, and search_tt_media_captions without opening 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?

Explicitly states the use case (find posts about a topic or brand) and names two alternative siblings with the conditions that select them (get_users_by_hashtag for accounts by hashtag, search_comments for comments). Routing is unambiguous.

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