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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely new behavior: the four-level verdict vocabulary (pass, weak, fail, not set), the separation of essential versus optional records, and the rule that BIMI and MTA-STS return 'absent' rather than 'failed'. It does not mention timeout, DNS resolution failure handling, or rate limits, so the operational envelope is only partly covered.

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?

Three sentences, each earning its place: what is checked, how results are graded, and when to reach for it. The core capability is stated in the first clause rather than buried.

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 carries the return-value burden and does so reasonably by defining the verdict labels and the 'absent' convention, which is enough for an agent to interpret results. Missing only secondary detail such as whether records include their raw values or which record is considered the 'essential' set.

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?

Only one parameter and the schema already documents it at 100% coverage with an example ('acme.com'). The description adds no meaning about the domain parameter (e.g. whether an email address, subdomain, or IDN is accepted), so this sits at the baseline for a fully documented single parameter.

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?

Names a specific resource (the six email-authentication records for one domain) and a specific action (check and judge each). The phrase 'in one call' implicitly separates it from the per-record siblings check_spf, check_dkim, check_dmarc, check_bimi and check_mta_sts.

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 concrete triggering scenario ('someone has been told to fix their email authentication and does not know which record that means'), which is more useful than a generic 'use when you need auth info'. It never explicitly says to prefer this over the individual check_* tools or when a single-record check is the better choice, so it stops short of full routing guidance.

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