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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=true, so safety is covered. The description adds non-obvious output behavior beyond that: a letter grade plus a per-failure reason and remediation fix, which tells the agent what it gets back and that partial failures are expected rather than errors.

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?

One front-loaded sentence with the action first and the enumerated checks after. The 11-item list is long but earns its place by telling the agent the exact coverage; nothing is redundant.

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?

No output schema exists, so the description must carry return-value information, and it does: grade, per-check reason, and per-check fix. Combined with annotations covering safety, an agent has enough to call it correctly without further context.

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?

There is a single parameter with 100% schema description coverage ('Domain (example.com)'), so the schema already carries the semantics. The description adds nothing about accepted formats (subdomain vs apex, IDN, trailing dot), so the baseline of 3 is appropriate.

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 gives a specific verb and resource ('Grade a domain A to F') and enumerates the 11 checks, so an agent knows exactly what this tool evaluates. It does not name or contrast with siblings like dns_report or the individual spf_lookup/dmarc_check tools, but the enumerated check list effectively signals it is the umbrella/aggregate report.

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?

Usage is only implied: the breadth of the 11 checks suggests 'use this for a full sweep, use the individual check tools for single concerns', but the description never states when to prefer this over dns_report or a targeted checker. No prerequisites, exclusions, or alternative routing are given.

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