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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, and the description goes well beyond them: it discloses per-row billing, that `limit` caps both rows and cost, and that the payload is user-generated content to be treated as untrusted. The billing/prompt-injection disclosures are exactly the kind of context annotations cannot express.

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 with no filler: ranking dimensions first, then routing guidance, then the sibling exclusion, then return shape and billing. Front-loaded and every clause carries information the agent needs.

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, so the description correctly enumerates the returned columns (pk, username, full_name, is_verified, follower_count, media_count). Combined with the cost model, the untrusted-content warning, and the Instagram-only exclusion, an agent has everything needed to call this correctly and interpret the result.

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; the description adds real meaning on top by mapping enum values to backing fields (`hearts`→heart_count, `videos`→video_count) and by tying `limit` to cost. It adds little for min_followers and verified_only beyond the schema, which keeps it at 4 rather than 5.

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 TikTok accounts by followers... or video count') and enumerates the ranking dimensions precisely. It explicitly distinguishes itself from siblings: 'use `search_tt_users` to find accounts by name' and notes that country/category/demographic filters belong to the Instagram-only `get_top_users`. An agent can route between the three 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?

Explicit when-to-use ('find the biggest TikTok creators'), an explicit alternative with its selecting condition ('search_tt_users' for name lookup), and an explicit exclusion (country/category/demographic filters exist only for Instagram via get_top_users). Both the positive and negative routing cases are covered.

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