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

Annotations provide readOnlyHint=false, idempotentHint=true, and openWorldHint=true, and the description earns credit by explaining why: it may scan once if no report exists (the side effect behind readOnlyHint=false), repeated calls return the same stored report, and `scanned_at` lets the agent judge staleness. It also reveals the cost profile ('cheap read') and that the world changes over time, whichcoheres with openWorldHint. No contradiction with the 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 front-loaded with the critical routing decision and delivers high-value information about the report's contents and staleness signal. However, it is mildly repetitive: the cheap look / cheap read / right default for a first look triad restates the same idea, and the final 'Prefer scan_domain' sentence largely repeats the opening conditional.

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 one-parameter tool with a rich output schema and meaningful annotations, the description covers everything an agent needs: what triggers a scan, what the wrapper includes (seven checks plus `scanned_at`), and when to pick the sibling instead. The presence of an output schema means the return structure need not be spelled out, and the staleness caveat is explicitly delegated to the agent.

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 coverage is 100% and the single `domain` parameter is already fully documented in the schema (registrable names and subdomains both work, no scheme/path/port, unicode normalized to punycode). The description adds no per-parameter meaning 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?

The description opens by placing the tool relative to scan_domain and then states a specific action: 'Return the stored report for a domain, scanning once only if none exists yet.' It names the concrete resource (the seven-check domain report) and enumerates the checks (SPF, DKIM, DMARC, MX, DNS hardening, expiry, blacklist), which makes the operation unmistakable and distinct from sibling tools.

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 description gives explicit routing rules in both directions: use get_report when a recent report is enough, use scan_domain when the state must be re-read now, with a concrete example ('after a DNS change'). It states the selection condition, the alternative, and the trade-off (cheap vs. fresh), leaving nothing to inference.

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