x_timeline_mentions

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

Annotations already declare readOnlyHint=true and destructiveHint=false, but the description adds significant value by disclosing that output is 'compact, sanitized' and by warning that mentions are a common prompt-injection vector and should be treated as data, not instructions. This is exactly the kind of behavioral context that helps an agent handle the tool safely.

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?

Two sentences with no filler. The first sentence states the purpose and default; the second conveys the output format and an important security consideration. All content is useful and front-loaded.

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?

Given the tool's moderate complexity, the presence of a full output schema, and annotations covering read-only and non-destructive behavior, the description is complete. It covers purpose, scope, output characteristics, and the key prompt-injection risk with no missing operational details.

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?

The schema already documents all six parameters with 100% coverage, so the baseline is 3. The description adds value by clarifying the default user behavior and by characterizing the default output as a 'compact, sanitized page,' which amplifies the meaning of the 'raw' parameter. This goes slightly beyond what the schema alone provides.

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?

The description names a specific verb ('Read') and resource ('posts mentioning an X user'), which clearly distinguishes this from sibling tools like x_timeline_home or x_timeline_user. It also adds a meaningful qualifier about third-party content, so there is no ambiguity about what this tool returns.

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?

The description clearly states the tool's scope and default behavior ('defaults to the authenticated user'), making it obvious when to use it. It does not explicitly name alternative tools or exclusion conditions, but the 'mentions' framing provides sufficient contextual guidance.

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