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

Adds behavior the annotations do not carry: malformed addresses are rejected with 400 and are uncharged, pricing is $0.01/call via x402 USDC or a card key with 25 free calls, failed calls are free, and repeated calls are billed again (which explains idempotentHint=false). The only redundancy is 'reads or computes only and changes nothing', which merely restates readOnlyHint=true and destructiveHint=false.

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 and its returned fields, then usage, then error/pricing caveats — a sensible priority order with no filler sentences. It runs slightly long by folding example, pricing, and payment rails into one block, but every clause carries information an agent can act on.

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, the description must convey return content, and it does name the key fields (bytecode size, proxy flag, implementation). Combined with error semantics and cost model, an agent has enough to call it correctly; only the exact response shape is left unspecified.

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% and the single parameter is self-explanatory, so the schema does the heavy lifting. The description still adds a concrete well-formed example address, which helps an agent format the 0x input correctly, though it does not discuss checksum or case handling.

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 an address on HyperEVM is a contract or a wallet) and goes further by naming the exact payload: bytecode size, EIP-1167 minimal-proxy status, and implementation address. The chain qualifier 'on HyperEVM' cleanly separates it from the ~20 other *_is_contract siblings without needing 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?

Gives an explicit trigger ('Use before sending funds or approving a spender') and an explicit alternative for a different need ('for a fuller risk verdict use check_counterparty'). An agent knows both when to pick this tool and when to route elsewhere.

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