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

Beyond the annotations (readOnly, openWorld, non-idempotent, non-destructive), the description discloses error handling ('malformed address is rejected with 400, uncharged'), pricing ($0.01/call via x402 USDC or a card key, first 25 free, failed calls free), and the billing consequence of non-idempotency ('each call is charged, so repeats are not free'). That is exactly the extra context annotations cannot carry, and it is consistent with them.

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?

Purpose and return content are front-loaded, and the pricing/error sentences carry real decision value. The closing clause 'Reads or computes only and changes nothing' partly restates readOnlyHint=true and could be trimmed, keeping it just short of full marks.

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 still describes what the call returns (contract-vs-wallet determination, bytecode size, minimal-proxy detection and implementation). Combined with cost, error behavior, and the alternative for deeper risk analysis, an agent has everything needed to call 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?

There is a single parameter with 100% schema description coverage, so the schema already documents 'address'. The description only adds a concrete example value, which is mildly useful for format confirmation but adds no new semantics such as checksum requirements or accepted address forms.

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?

The description names a specific verb (check), the resource (a 0x address on zkSync Era), and the outcome domain (contract vs. plain wallet), then enumerates what is returned: bytecode size and EIP-1167 minimal-proxy status plus implementation. An agent can distinguish this from other chain-prefixed siblings and from generic proxy tools 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?

It gives a concrete when-to-use ('before sending funds or approving a spender') and routes to a named alternative ('for a fuller risk verdict use check_counterparty'). It does not clarify its boundary against the sibling zksync_proxy, which also surfaces proxy information, so the routing is strong but not exhaustive.

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