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

Annotations already cover readOnly/idempotent/openWorld, but the description adds substantial context beyond them: the upstream resolver (Cloudflare DoH at 1.1.1.1), that nothing is stored, the $0.01 USDC x402 cost with the payment field location, and that invalid input or upstream failure is uncharged. This is exactly the behavioral detail annotations cannot convey.

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?

Three dense sentences with no filler: capability, routing to the sibling, then execution/cost semantics. Front-loaded with the primary purpose and every clause carries 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?

With no output schema, the description still communicates what is returned ('plain-English findings' plus the enumerated record types) and the full execution profile. Nothing an agent needs to invoke 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?

Only one parameter and schema description coverage is 100%, so the schema already fully documents 'domain' with examples. The description adds no additional syntax or format guidance beyond what the schema provides, making the baseline 3 appropriate.

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 the live DNS') plus the exact resource scope, enumerating the record types returned (NS, A/AAAA/CNAME, MX, SPF, DMARC, CAA, DNSSEC). It explicitly distinguishes itself from the sibling check_email_auth, so an agent can route correctly.

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 two concrete use cases ('DNS inventory' and 'debug resolution') and names the alternative tool with the condition that selects it ('for a deeper SPF/DMARC/DKIM/MTA-STS review'). Explicit when-to-use and when-to-use-something-else.

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