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

Annotations are sparse (readOnlyHint=false, openWorldHint=true, idempotentHint=false, destructiveHint=false). The description adds crucial behavioral detail: the cache-first dedup window of about a minute, that scanned_at may predate a DNS change, and how to handle verification. It also notes fix_record generation and SPF being diagnose-only. No contradiction with annotations.

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?

The description is long but each sentence earns its place: trigger conditions, the seven checks, cache behavior, and sibling differentiation. It's front-loaded with the usage trigger, and while it could be slightly tighter, the length is justified by the tool's complexity and the need to convey the dedup caveat.

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?

Given the tool's complexity (seven checks, cache semantics, fix_record, sibling overlap), the description covers all necessary aspects: what it does, what the report contains, how to interpret stale data, and when to use an alternative. An output schema exists, so return-value details are covered there, leaving the description to handle selection and behavioral caveats, which it does completely.

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?

The single parameter 'domain' already has a thorough schema description (coverage 100%) covering examples, subdomains, excluded scheme/path/port, and Unicode normalization. The tool description adds nothing about the parameter beyond what the schema already states, 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 states a specific verb ('scan') and a specific resource ('a domain'), and enumerates the seven deterministic checks it performs. It clearly distinguishes itself from sibling tools like get_report by explicitly framing itself as the fresh-scan tool, so an agent can tell them apart.

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 an exhaustive list of trigger phrases ('check, audit, diagnose, troubleshoot...') and explicitly contrasts with get_report: 'Use this when you need current state; use get_report when a recent cached answer will do.' This is a textbook example of when/when-not guidance with named alternatives.

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