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

Goes well beyond the readOnly/idempotent/non-destructive annotations by disclosing cost ($0.04 USDC via x402), the failure mode ('if no domain can be scored it errors and is not charged'), and result ordering (lowest score first). Those are exactly the non-obvious traits an agent needs before spending money on a call.

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 tight sentence with the capability front-loaded and the cost/error caveat appended as a parenthetical. No filler or restated title.

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?

Covers the score/grade/findings return shape in lieu of an output schema, plus cost and error/charge behavior. For a one-parameter paid read tool, nothing an agent needs to call it safely 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% and the schema already says '2 to 5 comma-separated domains', which the description repeats rather than extends. No extra guidance on delimiter handling, duplicates, or partial-failure semantics per domain; 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 ('Score 2 to 5 domains' email security in one call') and explicitly equates the output to the sibling email_security_score (SPF/DMARC/DKIM/MX score, grade, findings). The '2 to 5' bound implicitly separates it from the single-domain and bulk siblings, so an agent can pick it without opening a 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?

The '2 to 5 domains in one call' framing plus the reference to 'the same ... score as email_security_score' tells the agent this is the batch form of that sibling. It does not explicitly state when to prefer bulk_email_security_score instead, so the multi-sibling routing is inferred rather than spelled out.

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