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

Annotations already cover read-only (readOnlyHint=true) and open-world (openWorldHint=true). The description adds valuable behavioral context by stating that null is returned for unregistered names or missing address records, and provides a concrete example. This goes beyond what annotations provide.

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 description is two sentences: the first explains the action and return behavior, the second gives a concrete example. It is front-loaded, concise, and every sentence earns its place with no redundancy.

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 simple one-parameter tool with no output schema, this description is nearly complete. It covers the core action, the null return condition, and an example output. Minor gaps include no mention of ENS subdomain support or address checksumming, but these are not critical for typical use.

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%: the only parameter 'name' already has a clear description and example. The tool description does not add any additional parameter semantics beyond what the schema provides, so the baseline score of 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 clearly states the tool resolves an ENS name to an Ethereum address, using a specific verb and resource. It does not explicitly distinguish from the sibling tool eth_lookup_address (likely reverse lookup), so it misses the top score for sibling differentiation.

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 usage context is implied: use this when you have an ENS name and need its address. However, there is no explicit guidance on when not to use it or mention of alternative tools like eth_lookup_address for reverse resolution.

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