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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so safety is covered. The description adds useful scope information by listing the record types examined and noting it produces fix recommendations, but it says nothing about latency, how many DNS queries it issues, or what a partial failure looks like.

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, zero filler, with the enumerated coverage front-loaded and the usage condition placed last. Nothing could be removed without losing information.

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, read-only diagnostic with no output schema, the definition covers what is checked and hints at the output ('scores' and 'lists what to fix'). A brief note on the report's structure or the absence of a schema would have closed the remaining gap.

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 explains that full URLs or email addresses are reduced to the domain and that omitting the DKIM selector tries common ones. The description adds no parameter-level meaning beyond that, so the baseline of 3 applies.

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?

The description names a specific verb and resource ('Scores a domain's email setup') and enumerates the exact checks performed (MX, SPF, DKIM, DMARC, MTA-STS, TLS-RPT, BIMI, blocklists). The clause 'Covers the whole email setup in one call' clearly separates it from the granular single-record siblings like mx_check or dmarc_check.

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 clear selection context: use this 'for a general email health question,' which implicitly contrasts with targeted single-record checks. It stops short of explicitly saying when not to use it (e.g., when you already know the specific record type to debug), so it is not a full when/when-not statement.

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