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

With no annotations, the description carries the burden and does substantial work: it discloses the data source and liveness ('read straight from Ethereum mainnet'), the non-error failure signal ('with found telling you when there is no record'), authentication ('No API key'), and cost/payment ('$0.005 per call, paid over x402 (USDC)'). The remaining gap is what happens if neither of the two optional parameters is supplied, which the description never addresses.

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 compact sentences, each with a distinct job: usage trigger, exclusions, then cost/auth. The trigger is front-loaded, and the pricing sentence is dense but earns its place because it tells the agent a real cost is incurred per call.

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 annotations and no output schema, the description still covers the data source, the bidirectional result, the 'found' flag, auth, and cost. It stops short of describing the response shape beyond the flag and of clarifying that at least one of the two empty-required parameters must be given, which is the one operational ambiguity left.

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 already documents mutual exclusivity ('Use instead of name'), so the baseline would be 3. The description earns a bump by specifying that reverse resolution returns the *primary* ENS name, a semantic detail absent from the schema, and by naming the 'found' output flag that signals an empty result.

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 (resolves) and resource (ENS name / address) and explicitly frames both directions: forward resolution and reverse resolution to the primary name. An agent can distinguish this from every sibling in the evm_* family 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?

Opens with an explicit usage trigger ('Use when an agent has a name where it needs an address, or the other way round, before it can act') and then names two concrete exclusions with their sibling paths: /v1/util/address for format validation and /v1/evm/is-contract for wallet checks. When-to-use, when-not-to-use, and the alternatives are all present.

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