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

Annotations cover the safety profile (readOnlyHint, destructiveHint=false), and the description adds real context the annotations do not: live mainnet reads, a concrete cost model ($0.01/call via x402 USDC or card key, first 25 free, failed calls free), and a note that repeats are not free — which explains the non-obvious idempotentHint=false. That is meaningful value beyond structured fields.

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 core purpose is front-loaded in the first sentence, with usage in the second and commercial terms last. It is slightly long — the closing claims 'reads or computes only' partially restate the annotations and the charge warning is repeated with the pricing sentence — but nothing is wasted enough to be distracting.

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 return-value burden and does so by naming the fields returned in each direction (address + avatar, or primary name). It does not state behavior for unresolvable names or addresses lacking a reverse record, which is the remaining gap for a single-param lookup.

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 single parameter is already documented as accepting either an ENS name or a 0x address for reverse lookup. The description only reinforces this with the vitalik.eth example, adding no syntax or format detail beyond the schema, 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?

The description names a specific verb (resolve / reverse-resolve), the resource (ENS names and addresses), and the exact data returned (wallet address and avatar, or primary ENS name). Both directions of the operation are stated up front, so the agent can tell it apart from generic lookup siblings such as dns_lookup or domain.

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 states concrete use cases: turning a name into a payable address, and showing a readable name for a counterparty address. That gives clear selection context, but no explicit exclusion or named alternative (e.g. when to prefer dns_lookup or evm_checksum instead).

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