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

Annotations already declare the safe read profile (readOnly, idempotent, non-destructive). The description adds genuinely new behavior: it is a paid call ($0.002), returns an x402/MPP request rather than the data directly, and refuses bad input before charging. Rate limits and latency are not covered, keeping it from a 5.

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-loaded with the when-to-use clause and the two lookup modes, and every sentence carries information. It is a dense single paragraph that could be segmented, but nothing is wasted.

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 paid, multi-step x402 tool with no output schema, the description explains the request URL, cost, response-schema availability, and validation behavior, which is everything an agent needs to invoke it correctly.

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% with both params described and patterned, so the schema already carries the semantics. The description restates the same examples (vitalik.eth, 0x...) and clarifies the two params are alternatives, adding only marginal value 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?

States a specific operation on a specific resource (ENS resolution on Ethereum) and names both directions: name→address via the Universal Resolver and address→primary name via reverse record. No sibling overlaps with the evm_* family, and an agent can tell exactly what it does 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?

"Use when you need ENS on Ethereum" gives clear context, and it distinguishes the two input modes (name= for forward, address= for reverse). It stops short of naming when-not-to-use or an alternative tool for other chain data, so no exclusions are provided.

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