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

Beyond the readOnlyHint annotation, the description discloses meaningful behavioral traits: opens/clicks are real (pixel + link-wrap) while forward detection is best-effort via IP-subnet diversity, and results are owner-scoped. This is exactly the kind of reliability caveat an agent needs before trusting the data.

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?

A single dense sentence that front-loads the resource and then lists return fields with no filler. It is long but every clause (fields, reliability caveats, scoping) carries information.

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 compensates by enumerating the return fields and flagging which are reliable. Combined with the readOnlyHint annotation, an agent has enough to call it correctly; only explicit sibling routing is 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 is 100% and the schema already explains message_id is a UUID from mAYL_send or inbox, so the description adds nothing new about the parameter. Baseline 3 applies when the schema does the work.

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: engagement summary for one sent email identified by message_id, then enumerates the exact fields returned. The 'one sent email (by message_id)' scoping implicitly separates it from aggregate siblings like mAYL_metrics and mAYL_list, though no sibling is named explicitly.

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 required message_id and the note that it comes 'from mAYL_send or inbox' implies the usage context. 'Owner-scoped' signals an access prerequisite, but there is no explicit when-to-use / when-not-to-use guidance or named alternative (e.g. vs mAYL_metrics for aggregates).

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