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

Annotations already declare readOnly/idempotent/openWorld=false, and the description still adds meaningful behavior: it operates only on loaded lists with no DNS lookup, and discloses the resulting gap that check_email covers. This is genuine context beyond structured fields, though pagination/volume behavior is not mentioned.

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?

Purpose and classification categories are front-loaded, and the operational limitation and alternative follow logically. It is dense and somewhat run-on, packing enumerations into long clauses, but little is wasted.

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 carries the burden of explaining return semantics and does so by enumerating result categories plus the harvester observation timestamp. It leaves the exact result format unspecified, but the agent has enough to invoke and interpret it.

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 parameter's schema already documents that it accepts a domain or an email address. The description's 'Accepts a domain or an email address' merely restates the schema, so the baseline 3 applies with no added syntax or format detail.

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 (look up / says whether) against a specific resource (a domain on SignupBouncer's burner/relay/free-subdomain lists). It explicitly enumerates the classification outcomes and separates itself from check_email for the case of brand-new burner domains.

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?

Names a sibling (check_email) and the condition under which that sibling is required: brand-new burner domains on a burner mail server. It gives clear context for when this lookup suffices, though it doesn't cover other sibling boundaries such as get_rules or explain_reason.

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