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

Annotations only declare readOnlyHint and openWorldHint; the description adds meaningful behavior beyond them: live DNS lookups at request time, a few-second latency, guarantee of no stale records, the OK/WARNING/MISSING/ERROR status vocabulary, and how healthScore is computed (7-day inbox share). This is rich context an agent cannot get from structured fields.

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, front-loaded with what is checked before the usage hint and latency note. Dense but every clause carries information; the healthScore parenthetical is slightly long but justified since no output schema exists.

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 fully compensates by explaining the returned record statuses, human-readable issues, and warm-up fields (enrollment, ramp target, daily cap, healthScore). An agent has everything needed to call and interpret the result.

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% and the single id parameter is documented with its source (list_sender_emails). The description adds no parameter-level detail, so baseline 3 is appropriate when the schema fully carries that burden.

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 (checks) and specific resources (SPF, DKIM, DMARC, MX records plus warm-up status) for the sender domain. It clearly distinguishes itself from siblings like get_sender_email_warmup and get_sender_reputation by enumerating exactly which signals it returns.

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?

Gives a clear use case ('Use it to diagnose deliverability'), which orients the agent. However, it never names when NOT to use it or routes to alternatives such as get_deliverability_insights or get_sender_email_warmup, so selection among similar siblings still requires inference.

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