Summary by sender

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

The description discloses that the scan is cached for the session, which is useful behavioral information beyond the readOnly and idempotent annotations. It also clarifies that it scans a whole folder by default, implying no destructive or state-changing side effects. No contradiction exists with the provided annotations.

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 compact and informative, covering behavior, sorting, caching, and suggested follow-up actions. The opening phrase 'KEY TOOL FOR TRIAGE' is a minor stylistic flourish rather than essential information, but it does not detract much from overall clarity.

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 description adequately covers the scanning behavior, default folder, summary fields, sorting, caching, and follow-up tools. Since an output schema exists, the description does not need to detail return structures, and no important context appears missing.

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 for parameters is 100%, so the baseline is 3. The description mostly restates the folder default and does not add meaningful semantics beyond the schema descriptions for top, since, or folder. Thus the description does not significantly enhance parameter understanding.

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 clearly states that the tool scans a folder and aggregates messages by sender, which distinguishes it from siblings like mail_search, mail_get_message, and mail_bulk_by_sender. It also specifies the summary contents: count, unread, latest message, and unsubscribe method. This makes the tool's purpose unambiguous.

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 frames the tool as a key triage tool and suggests follow-up actions with mail_unsubscribe and mail_bulk_by_sender, giving useful workflow context. It does not explicitly state when to prefer this over mail_search or mail_list_folders, but the purpose is clear enough for an agent to choose appropriately.

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