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

Annotations already declare destructiveHint=true, openWorldHint=true, and idempotentHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: the send is self-scoped to the caller's own address and routed through the workspace's own Resend, which tells the agent the blast radius is one mailbox. It does not mention rate limits or failure behavior, keeping it short of a 5.

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 tight sentences with zero filler, front-loaded with the action and recipient before the optional reply-verification detail. Every clause earns its place.

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 two-parameter tool with no output schema, the description covers what it does, to whom, and why, and the confirm-gate behavior lives in the schema. What is missing is routing against the near-identical test-send siblings, which is the one thing an agent selecting this tool actually needs.

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 50%: 'confirm' carries a rich schema-side description of the confirm-first workflow, while 'stream' is enum-only. The description paraphrases the stream values ('support or marketing email') but adds no new semantics, so this lands at the baseline for partial coverage.

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 concrete verb+resource ('Send a test support or marketing email') and scopes the recipient precisely ('the signed-in person's own account address, through the workspace's own Resend'). That self-scoping distinguishes it from broadcast siblings, but the description never names the overlapping alternatives (send_support_inbox_test, send_test_newsletter), so differentiation is inferential rather than explicit.

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?

It gives the purpose ('to prove the setup works') and a follow-up action ('replying to the support test checks that replies come back'), which implies when to use it. It offers no when-not guidance and does not address the several sibling test-send tools, leaving the agent to guess when this is preferred over send_support_inbox_test or send_test_newsletter.

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