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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds useful context that the data comes from public DNS and a live lookalike-domain lookup (explaining the open-world behavior) and that output is an A-F grade with findings. It does not mention latency, rate limits, or behavior on malformed/unresolvable domains.

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?

A single front-loaded sentence with no filler; the what, the sources, and the return shape all appear in one pass. Nothing repeated from the title is wasted beyond a brief restatement.

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 read-only single-parameter tool with no output schema, the description supplies the missing return semantics (A-F grade plus findings) and names the evidence domains inspected. Slightly incomplete on failure modes and timing for the live lookalike lookup, but nothing essential to invocation is absent.

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 schema description coverage is 100% — the schema already defines 'domain' with an example. The description confirms the domain is what gets graded but adds no format constraints, normalization rules, or edge cases beyond the schema, 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?

States a specific verb and resource ('grade how exposed a domain is to email spoofing and business email compromise') plus the evidence sources (SPF, DMARC policy strength, alignment, live lookalike domains). This clearly separates it from siblings like check_bimi or check_blacklist, which cover adjacent but different checks.

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?

The intent is implied — run it on a domain to assess spoofing/BEC exposure — but there is no explicit when-to-use versus when-not guidance, and no routing to alternatives such as check_bimi for BIMI-specific posture or check_blacklist for reputation. An agent can infer the use case but must reason about sibling selection unaided.

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