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

Annotations already declare readOnly=false, openWorld=true, idempotent=false, destructive=false, so the safety bar is lower. The description adds genuine context beyond them: the non-dry_run mode mails real recipients, and dry_run validates recipients without sending — a behavioral choice the annotations do not express. It does not mention whether repeated calls resend, quota impact, or delivery/response behavior.

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?

Two sentences, both earning their place: purpose first, safety escape hatch second. No filler, no restatement of the title, and the most important qualifier ("before the actual send") is front-loaded.

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 3-parameter tool with full schema coverage and annotations present, the description covers purpose and the dry-run path. It leaves open whether test recipients must come from a testmail group (list_testmail_groups exists as a sibling), whether a test send counts toward campaign state, and what the call returns — gaps that matter for a real-world sending operation with no output 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 all three parameters are already documented in the schema; baseline is 3. The description restates dry_run's semantics ("validate the recipients without sending") and frames recipients as test recipients, but adds no format, limits, or constraints beyond what the schema provides.

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 ("Send a test email for a campaign") plus the scope ("to specified recipients before the actual send"). It is clearly distinguishable from generic send tools, though it does not name its closest siblings (send_personalized_email, send_transactional_email) to draw the contrast 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?

"Before the actual send" implies the intended moment of use, and the dry_run sentence gives a concrete safe-path instruction. However, there is no explicit when-not guidance, no mention of when to prefer send_personalized_email or send_transactional_email instead, and no statement of whether dry_run is recommended as the default first step.

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