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

Annotations already declare readOnlyHint and openWorldHint, yet the description adds substantial context beyond them: reverse resolution is only accepted when the name resolves back to the same address, which text records are returned when set, the null-address not-found behavior, and the $0.002 USDC x402 price with failed calls not charged.

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?

Front-loads the core resolution behavior, then layers record coverage, not-found handling, and pricing in short declarative sentences with no filler. Every sentence carries operational information.

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?

Output schema covers the return shape, and the description still covers the edge cases an agent needs (null address on unregistered names, forward-confirmation requirement, paid-call pricing and non-charging on failure). Nothing material is missing for correct invocation.

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%, so the baseline is 3, but the description adds real semantics beyond 'ENS name' and '0x…': it explains the two parameters are alternative input modes with different resolution directions and that address results are validated by reverse lookup. It stops short of saying whether both may be supplied together.

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?

Opens with a specific verb and resource ('ENS on Ethereum mainnet') and describes bidirectional resolution (name→address, address→primary name) with the forward-confirmation rule. That behavior is distinct from siblings like evm_address, address_parse, and dns, so an agent can discriminate 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?

Explains how to drive the tool: supply a name to get an address, or an address to get the primary name, and clarifies that an unregistered name returns 200 with address null. It does not name an explicit alternative or exclusion (e.g., when to prefer evm_address), so it falls short of a 5.

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