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

Annotations cover the safety profile (readOnlyHint=true, openWorldHint=true), but the description adds genuinely useful behavior: pagination contract (has_next_page + next_cursor), ordering (newest first), and a precise credit cost (13 per tweet, min 15, waived on bulk). This is real context beyond the 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?

Three tight, front-loaded paragraphs — purpose, pagination, cost — each earning its place with zero filler or repetition of the structured fields.

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 usefully sketches the return shape (cursor fields) and cost model, which is what an agent needs to page correctly. It is slightly short on userName input semantics, but otherwise complete for a two-parameter read tool.

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 0%, so the description has to carry parameter meaning. It explains cursor usage well ('pass next_cursor as cursor for more'), but says nothing about the required userName format (handle vs. ID, leading @), leaving half the parameters under-documented.

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 ('Return posts that mention a user') with scope ('newest first') and a clarifying frame ('the account's inbound conversation'). This distinguishes it implicitly from reply/timeline siblings, but it never names an alternative tool explicitly, so it lands at 4 rather than 5.

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?

There is no explicit when-to-use or when-not-to-use guidance. The description never references the many adjacent siblings (tweet_replies, user_tweet_timeline, search), so an agent must infer the boundary between 'mentions' and 'replies' on its own.

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