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

Annotations already declare readOnlyHint and openWorldHint, so the safety profile is covered. The description's metric list adds real value given there is no output schema, but it does not say whether figures are counts or rates, how fresh the data is, or that a nonexistent mailing_id errors.

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?

One front-loaded sentence with a compact metric list; every element earns its place. It is a noun phrase rather than a verb-led statement, which slightly weakens the opening.

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 simple single-parameter read with no output schema, the enumeration of returned metrics substantially fills the gap. Missing only data-freshness and error-behavior notes.

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% with a single documented mailing_id, so the schema carries the parameter burden. The description adds no syntax, scoping, or validity notes beyond what the schema already states.

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?

Names a specific resource (one mailing's response summary) and enumerates the metrics it covers, so an agent can tell it apart from emma_get_mailing (settings/details) or emma_get_response_summary (broader summary). It never explicitly contrasts those siblings, though, so the differentiation is inferential.

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?

Usage is only implied: 'of one mailing' plus the required mailing_id signal a per-mailing report. There is no statement of when to prefer this over emma_get_response_summary or emma_list_mailing_activity, and no prerequisites or exclusions.

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