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

Annotations already declare readOnly, openWorld and idempotent, yet the description adds real value beyond them: live registry/DNS/RPC queries, 1-5 s typical and ~12 s worst case, partial results with failures surfaced under errors, local-blocklist-only reputation with the explicit caveat that no match is not a clean bill of health, and no query logging.

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?

Two dense paragraphs, front-loaded with the resource list and result summary before routing advice and behavior. Slightly long, and the per-resource fact-sheet enumeration borders on cataloging, but every sentence carries decision-relevant information.

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?

Output schema exists and the description still notes the trailing details_url provenance link. Combined with live-query timing, partial-failure handling and reputation caveats, nothing an agent needs to call this correctly or interpret the result 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 coverage is 100%, so the baseline is 3, but the description goes further by tying each accepted query form to the result shape the agent will get back (registrar/dates/DNS vs. network owner/ASN/geo vs. Web3 registration), which helps the agent decide what to pass. The namespace parameter itself is not discussed in the description, so it is not a full 5.

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?

Names a specific verb ('look up') plus every resource class it accepts (domain, IP, CIDR, ASN, Web3 name) and states the returned artifact ('compact fact sheet'). An agent can distinguish it from check_lookalike or check_mail_security 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 routing: 'use it first for any question about who owns, runs, hosts or registered something,' then names both alternatives with the condition that selects them (check_mail_security for per-check detail, check_lookalike for bulk screening without network calls). Both when-to-use and when-to-prefer-something-else are covered.

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