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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely non-obvious operational context: a $0.002 USDC charge per successful call, the x402 payment rail (Base, Solana, Arc), and that failed calls are not charged. This is exactly the kind of cost/auth detail an agent needs before invoking. Minor gap: the phrase 'Public free API' sits slightly awkwardly next to the per-call price (it describes the upstream registry, not this wrapper) and invalid-MAC behavior isn't described.

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 tight sentences: purpose and source first, scope limit second, cost/payment last. Nothing is redundant and the most decision-relevant facts are front-loaded.

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?

An output schema exists, so return-value detail is unnecessary. The description covers source, scope, cost, payment mechanism, and billing on failure — everything an agent needs to decide to call a paid single-lookup tool with one required parameter.

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 single parameter already documents both accepted forms with examples. The description repeats 'MAC address or OUI prefix' without adding format, normalization, or case-sensitivity guidance beyond what the schema provides, so 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+resource (MAC address vendor lookup) and the exact output (registered hardware vendor for a MAC address or OUI prefix), plus the underlying data source (IEEE OUI registry via macvendors.com). No sibling tool overlaps this domain, so the agent can immediately tell this is the only relevant choice.

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 description makes clear the input domain (MAC or OUI prefix) and explicitly bounds the result (vendor name only, no device data), which tells an agent when this tool is and is not sufficient. It stops short of naming alternatives or stating when to avoid the tool, so it falls short of a 5.

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