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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds value beyond that by disclosing the diagnostic scope and that output includes both what is wrong and remediation guidance, which tells the agent what it will get back. It does not mention latency, rate limits, or external lookups despite being an open-world call.

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 the capability and followed by the trigger condition, with no filler. The run of eight protocol acronyms is dense but each one contributes to matching the agent's task vocabulary, so little is wasted.

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 one-parameter read-only diagnostic with no output schema, the definition covers scope, checks performed, and the shape of the answer (problems plus fixes), which is sufficient to call it correctly. It leaves unstated how the result relates to the sibling report-link tool or whether results are cached, minor gaps at this complexity level.

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 schema already documents the single domain parameter including that a URL or email address is acceptable. The description adds no extra semantics about the parameter beyond implying domain scope, so the baseline of 3 applies since the schema carries the 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 concrete verb and resource ('check a domain's email deliverability') and enumerates the records inspected (MX, SPF, DKIM, DMARC, MTA-STS, TLS-RPT, BIMI, blacklists), which clearly sets it apart from check_email_record at the domain-vs-record level. It does not explicitly name or contrast with siblings like get_full_report_link, so it stops short of full sibling differentiation.

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?

Provides explicit triggering contexts: 'why their emails go to spam, aren't delivered, or whether their email setup is correct.' That gives an agent a clear when-to-use signal. There is no when-not-to-use clause and no named alternative for cases like inspecting a single address, so it is strong but not exhaustive.

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