chain_ens

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

Annotations already declare readOnlyHint, idempotentHint, and openWorldHint, and the description does not contradict them — it confirms "read-only." Beyond annotations, it discloses the payment model (x402 USDC on Base or free with an API key) and explains that an HTTP 402 contains a decoded price quote rather than being a failure, which is exactly the non-obvious behavior an agent needs to avoid misinterpreting the response.

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 definition is front-loaded with the core purpose, followed by an example and then operational behavior. The "either direction" phrasing and the subsequent "Use when you need to resolve..." sentence repeat the same point slightly, but the overall text is efficient and every remaining sentence adds value.

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?

For a two-parameter read-only lookup with no output schema, the description covers purpose, directionality, an example, payment behavior, and the 402 response semantics. It does not explicitly state the return shape (e.g., resolved address string vs. primary name), though the bidirectional framing strongly implies it, leaving a minor gap.

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%, so the schema already explains both parameters, including optionality and the name-or-address requirement. The description adds directionality and a concrete `/v1/chain-ens?name=vitalik.eth` example, but it does not clarify the schema's internal inconsistency between `required: ["name"]` and the `name` field being marked optional. Baseline 3 is appropriate.

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 and resource — ENS lookup on Ethereum mainnet — and explicitly covers both directions (name→address and address→primary name). It also rules out the adjacent non-ENS lookup case, so an agent can distinguish it from chain_balance, chain_tx, and other chain siblings without opening the 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?

It gives a clear when-to-use statement (resolving ENS names or reverse-resolving addresses) and an explicit exclusion ("Not for non-ENS lookups"). It stops short of naming an alternative sibling, but there is no other ENS tool in the sibling list, so the routing guidance is effectively complete.

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