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

Annotations already cover read-only, non-destructive and open-world behavior, so the bar is lower. The description adds two things annotations cannot: the returned field set (username, display name, user ID, verification/privacy status, picture) and the per-request billing cost of $0.006, which is materially useful for call budgeting.

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?

Three short sentences, front-loaded with the core action, followed by return fields and the disambiguating alternative. No filler; each sentence carries distinct information.

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 fields, and it adds cost and alternative-tool context. A brief note on result limits or pagination would make it fully complete, but it is sufficient to invoke 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?

Only one parameter and schema description coverage is 100%, so the schema already documents the keyword and its 500-character limit. The description restates 'by keyword' without adding format or syntax guidance, so baseline 3 applies.

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) plus resource (Threads users) and scoping mechanism (by keyword), and explicitly contrasts with threads_user_profile for single-account lookups. An agent can distinguish it from search_threads and threads_user_profile without opening schemas.

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 routes single-profile lookups to threads_user_profile, which is the key alternative. It does not state exclusions relative to the other search_* siblings (e.g., search_threads for posts), but the context is clear.

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