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

Annotations already cover the safety profile (readOnly, openWorld, non-destructive), and the description adds what they cannot: pay-per-call pricing, the payment protocol, a no-charge guarantee when a data source is down, and the behavior of an unpaid or invalid call. This is exactly the billing/failure context an agent needs before invoking a paid endpoint.

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?

The return payload is front-loaded and the alternative-routing and pricing details follow in short sentences. The parenthetical enumeration is dense but every item is informational; only minor tightening is possible.

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 full burden of describing returns and does so by listing the snapshot fields and the changed-since-last-check flag. Combined with pricing and failure-charging behavior, an agent has everything needed to call it correctly.

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 schema itself documents the normalization behavior ('An email address or URL is reduced to its domain'). The description adds nothing about the domain parameter, so it neither compensates nor detracts; 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 ('fresh public snapshot of a supplier domain') and enumerates exactly what the snapshot covers (site status, registrar, DNS, MX/SPF/DMARC, trust verdict) plus a change flag. It also explicitly distinguishes itself from the sibling vendor_what_changed, so an agent can route without opening schemas.

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?

It names the alternative explicitly ('Use vendor_what_changed for the full diff'), giving a clear conditional for choosing between the two. It does not address the other nearby siblings (vendor_trust_score, domain_rdap_lookup, email_auth_check) that overlap in coverage, so the routing guidance is clear but not exhaustive.

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