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

Annotations already declare readOnly/idempotent/openWorld, but the description goes further: 1-hour per-domain caching, 25 free lookups per IP per day with a paid key in the x-api-key header, one lookup charged per domain, nothing stored and no email sent, plus the blocked=true and exists flags for edge cases. That is exactly the operational context annotations cannot express.

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?

Front-loaded with purpose, then routing guidance, then input, then the return shape and limits. The enumeration of return fields is long, but it is load-bearing because no output schema exists, so nearly every sentence 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?

With no output schema, the description fully specifies the return payload (check/results[0], technologies, email, dns, securityHeaders, registration, files, summary, analyzedAt, cached) and covers limits, auth and edge cases like bot-blocked sites. Nothing an agent needs to call it correctly is missing.

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%, so the single domain parameter is already documented including the URL/email examples. The description restates the accepted input forms and adds only the 'one domain counts as one lookup' constraint, which is billing context rather than parameter semantics. 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 and resource ('Everything about ONE domain in a single call') and immediately scopes it against the sibling tools email_security, tech_stack and domain_registration. An agent can pick this tool without opening any schema.

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?

Gives explicit when-to-use scenarios (sales research, vendor or security review, due diligence) and an explicit when-not: several domains or a single aspect should route to the cheaper siblings. Alternatives are named with the condition that selects them.

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