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

Goes beyond the annotations (which already declare read-only/idempotent/non-destructive) by disclosing the resolution verification semantics, that lookups hit Ethereum mainnet, the cost ('free', errors 'not charged'), and the failure contract (isError on invalid input or upstream failure). Missing only rate-limit/caching nuance, so just short of a 5.

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?

Front-loaded with the core purpose and each sentence carries distinct information (records, network, verification, price, errors). The parenthetical verification clause and semicolon-chained pricing/error note make it slightly dense for a one-parameter tool.

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 an output schema present and 100% param coverage, the description supplies everything else an agent needs: input forms, network, verification behavior, cost, and error semantics. Nothing material is missing for correct invocation.

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% with a single well-described 'query' param, so the baseline of 3 applies. The description's 'vitalik.eth or 0x address' restates the schema without adding syntax or format detail beyond it.

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 bidirectional verb+resource: 'ENS name → address and address → primary name', plus the exact text records returned (avatar, twitter, github, url, email). Scoping to 'ENS on Ethereum mainnet' implicitly separates it from DNS/WHOIS siblings 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?

Usage is strongly implied by naming both accepted input forms ('vitalik.eth or 0x address') and the resolution direction, but there is no explicit when-to-use guidance and no named alternatives (e.g., dns_lookup, address_check). Adequate but leaves the agent to infer routing.

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