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

Goes well beyond the annotations: scope limited to public signals, no charge when a data source is down, $0.01 USDC per call via x402 on Base, unpaid calls return the payment requirement, and invalid input is free. These are exactly the billing and failure-mode facts an agent needs before invoking a paid endpoint, and nothing contradicts readOnlyHint/destructiveHint.

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?

Four tight sentences with the payload described up front and pricing pushed to the end where it belongs. The opening sentence is a long noun phrase without a main verb, which slightly slows parsing, but no sentence is filler.

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 does the work of enumerating return fields, and it fully covers the payment path. The remaining gap is the baseline dependency: it never says what happens on a first call with no prior stored snapshot, which is material for a diff-style tool.

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?

Single parameter with 100% schema description coverage, and the schema already explains domain normalization (email address or URL reduced to its domain). The description adds no additional meaning about the domain argument, so the baseline of 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?

Concrete verb-and-resource: reports every field that changed at a supplier domain since the previous stored check, and enumerates the payload (before/after values, severity, summary, history, snapshot). It implicitly separates itself from vendor_watch_recheck and vendor_intelligence via the 'previous stored check' framing, though it never names the sibling that produces that stored baseline.

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?

Usage is only implied: the phrase 'since the previous stored check' hints that a prior check must exist, but the description never states that prerequisite or says when to use this versus vendor_watch_recheck or vendor_intelligence. No exclusions or alternatives are given, so the agent must infer routing from sibling names.

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