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

With no annotations, the description carries the full burden and does well: it discloses live mainnet reads, forward verification of resolutions, the exact cost ($0.002 USDC per call via x402), and an example return payload. It stops short of covering failure modes such as unresolvable or unregistered names and whether results are cached.

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?

Dense but front-loaded: purpose and directionality come first, then usage, pricing, and an output sample. The example JSON is compact and earns its space as the only output documentation, though the run-on colon-separated phrasing is slightly harder to parse than clean sentences.

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 no output schema, including a sample response is the right compensation, and pricing plus data-source disclosure covers the economics an agent needs before calling. The one gap is that neither parameter is marked required yet the tool needs exactly one; the description hints at this only through 'or' rather than stating the constraint explicitly.

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 parameters already described as name vs. reverse-lookup address. The description's examples ('name=vitalik.eth or address=0x...') add minor clarity about the either-or usage but no new semantics beyond the schema, so baseline 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?

States the specific verb and both directions of the resource: 'ENS lookup: name to address (with avatar) or address to primary name, with forward verification.' It also pins the data source ('live Ethereum mainnet'), which cleanly separates it from generic siblings like domain_lookup or url_dossier.

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 before sending funds to a human readable name' gives a concrete decision trigger an agent can act on. It lacks explicit exclusion guidance (e.g., when to prefer domain_lookup or token_preflight), 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.