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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful behavioral context by disclosing which external data sources the single call touches (WHOIS/DNS, SPF/DKIM/DMARC records, CT logs), which tells the agent to expect external lookups and a multi-source aggregate.

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 that leads with the action and scope, then enumerates coverage compactly. No filler, no repetition of the title, and every clause earns its place.

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?

An output schema exists, so return-value documentation is not required, and the description adequately signals the breadth of what one call returns. It is slightly thin on edge cases (invalid domains, partial failures, cost of a consolidated multi-source call), but complete enough for a one-parameter read tool.

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 description coverage is 100% and the single 'domain' parameter already carries a format example ('stripe.com'), so the schema does the heavy lifting. The description adds no further input semantics (e.g., bare domain vs URL vs subdomain handling), so the baseline 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 ('checks') and resource ('domain'), then enumerates the exact data categories returned: registration/DNS, email security, tech stack, and subdomain CT logs. The domain focus distinguishes it from brief_company and brief_place, though it does not explicitly contrast itself with brief_stack, which also covers tech stack.

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?

'One call checks a domain' implies this is the consolidated alternative to running several narrow lookups, which hints at when to reach for it. However, there is no explicit when-to-use statement, no exclusions, and no routing advice against the overlapping brief_stack sibling, leaving the selection decision to inference.

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