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

Annotations already declare readOnly/openWorld/idempotent/non-destructive, so the safety profile is covered. The description still adds real value beyond that: what the panel surfaces (country, verification details, username-change history) and the shape of the return ('a single profile object under `data`'). It does not mention auth or rate limits, but the annotation bar is met with useful extra context.

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 front-loaded sentences with zero waste: purpose, use case, return shape, and sibling routing in order of importance. The appended pricing block is boilerplate, not part of the authored description.

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?

An output schema exists, so return values need not be enumerated, yet the description still notes the `data` wrapper. For a one-parameter read tool with rich annotations, everything an agent needs to select and call it correctly is present.

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 single userName parameter is fully documented by the schema; baseline is 3. The description's 'by @handle' offers a marginally different framing than the schema's 'screen name' but adds no syntax or format detail beyond it.

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 + resource — fetch the extended 'About this account' panel for an X user by @handle — and explicitly contrasts it with the sibling get_twitter_user_info. An agent can distinguish this from the standard-profile tool 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?

Gives explicit when-to-use ('provenance and trust checks') and names the alternative with its selecting condition ('For the standard profile (bio, follower counts, avatar), use get_twitter_user_info instead'). Nothing is left to inference.

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