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

Annotations already declare readOnlyHint=true and destructiveHint=false, and the description reinforces that with 'Reads or computes only and changes nothing.' The valuable additions are the error contract (malformed address rejected with 400, uncharged) and the pricing model ($0.01/call, first 25 free, failed calls free, repeats not free), which explains the otherwise puzzling idempotentHint=false. It does not describe response shape at field level, but for a single-value read the disclosed error and billing behavior is the meaningful extra context.

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 capability, then usage, then error/billing notes — no sentence is filler, and the pricing clause justifies the non-idempotent hint. Slightly dense for one paragraph, but each clause carries information an agent would otherwise have to guess.

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?

No output schema exists, yet the description enumerates what is returned (bytecode size, proxy status, implementation address), plus error behavior, cost, and read-only semantics. For a single-address lookup tool, nothing essential to correct invocation is missing.

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?

With one parameter and 100% schema coverage, the schema baseline is 3, but the description adds genuine meaning: the required 0x format is illustrated with a concrete example address and the consequence of a malformed value (HTTP 400, no charge). That goes beyond the terse schema description '0x address'.

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 verb and resource ('Check whether a 0x address on Unichain is a smart contract or a plain wallet') and enumerates the exact outputs: bytecode size, EIP-1167 minimal-proxy status, and implementation target. This clearly separates it from the generic chain siblings and from unichain_proxy / check_counterparty.

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?

Gives an explicit use case ('Use before sending funds or approving a spender') and routes to an alternative ('for a fuller risk verdict use check_counterparty'). The implicit boundary against the sibling unichain_proxy is not spelled out, but the when-to-use condition is concrete enough that an agent can act on it.

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