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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), and the description adds genuinely new behavior: recipients are masked, and the two send counters differ because sentToday is a rolling 24-hour window while sharedTrial.sendsUsed is lifetime. It stops short of describing ordering, default page size, or what a record contains.

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?

Four short sentences, front-loaded with purpose and privacy behavior, then usage, then the counter-disambiguation, then a one-line negative guarantee. Nothing is filler and no sentence repeats a structured field verbatim.

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 does meaningful work by naming two return counters and disclosing recipient masking, which an agent needs to interpret results. It still leaves the per-delivery record shape and pagination behavior implicit, but for a simple two-parameter read tool this is close to sufficient.

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 50%: the 'project' parameter is documented in-schema, but 'limit' carries no description anywhere, and the description never mentions it (no default, no ordering implication). The discussion of sentToday and sharedTrial.sendsUsed explains response fields rather than parameters, so it does not compensate for the gap.

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 ('List recent email outcomes for this account') and enumerates the outcome states the listing surfaces, which is far more than a restatement of the name. It does not, however, distinguish itself from nearby read tools such as read_sending_status or read_integration_delivery_status that an agent could easily confuse it with.

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?

'use this to diagnose queued, delivered, opened, clicked, bounced, complained, or failed mail' gives a concrete diagnostic intent that tells the agent when the tool applies. There is no explicit exclusion or pointer to the sibling status tools, so overlap with read_sending_status and read_integration_delivery_status remains unresolved.

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