who_is_this

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

With no annotations, the description must carry the behavioral disclosure burden. It adds one useful trait: it does not retain message content. However, it does not explicitly state that the operation is read-only or that no state is modified, nor does it mention prerequisites, rate limits, or side effects. The 'no content' note is helpful but partial.

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?

The description is three short sentences, front-loads the core purpose, and every sentence contributes: purpose, output, and a key limitation. There is no filler or repetition, making it appropriately sized and well structured.

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?

For a 5-parameter tool with no required parameters and no output schema, the description gives the essential return fields (count, timing, reactions). It does not explain parameter selection logic, but the fully covered schema compensates for that. It is complete enough for an agent to understand the tool's role and invoke it, assuming it reads the schema.

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 tool description itself adds no parameter-specific meaning beyond the schema. It does not clarify the mutual exclusivity or alternatives between account/project or username/author_key, but the schema already covers these relationships. The description neither enhances nor detracts.

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 states a specific verb and resource: '返信する相手を確かめる' (check who you're replying to) and specifies the output: contact count, timing, and reactions. It also explicitly notes what it does not hold ('発言の内容は持たない'), distinguishing it from content-reading tools like thread_read. This clearly differentiates it from siblings.

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 implies the use case ('before replying') but does not explicitly state when to use this tool versus alternatives, nor does it mention exclusions or sibling tools. No structured guidance directs the agent to choose this tool over others, leaving usage context only implicit.

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