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

Annotations already mark the tool as read-only, idempotent, open-world, and non-destructive. The description adds meaningful behavioral context beyond annotations: pricing ($0.01 per call), payment mechanism (x402 on Base), prepaid credit-token header, free tier, and no wallet/API key requirement. This is exactly the kind of operational nuance annotations do not capture.

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, and the pricing/authentication details are useful rather than filler. However, the phrase 'Required input: query' repeats what the schema already states, making the description slightly less tight than it could be.

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 a single parameter, an output schema present, and safety covered by annotations, this description is operationally complete: it covers network, pricing, payment method, free tier, and authentication requirements. Nothing needed to call the tool correctly is missing.

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?

The schema already documents the single 'query' parameter as 'ENS name or address', giving 100% coverage. The description supplements this with concrete examples (vitalik.eth → address, address → primary ENS name) and clarifies the bidirectional nature of the lookup, adding real meaning beyond the schema.

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 states a specific verb ('Resolve') and resource (ENS names ↔ addresses on Ethereum mainnet), and explicitly calls out forward and reverse resolution. It also distinguishes itself from the Basename resolver for Base, which is a sibling tool.

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 gives clear usage context by specifying Ethereum mainnet and naming the Basename resolver as the complementary tool for Base. It does not provide an explicit 'when not to use' rule, but the network distinction is enough to guide tool selection among siblings.

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