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

Beyond annotations (readOnlyHint, openWorldHint, idempotentHint=false, destructiveHint=false), the description adds pricing details ($0.01/call via x402 USDC or card key, first 25 free, failed calls free), error handling (malformed address returns 400 uncharged), and clarifies that repeats are not free because each call is charged. It also explicitly states 'Reads or computes only and changes nothing,' reinforcing the read-only nature.

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?

The description is front-loaded with purpose and then covers usage, error handling, example, and pricing. It is generally efficient, but there is slight redundancy in repeating the charging policy near the end.

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?

Given the simple tool, one parameter, and no output schema, the description covers what is returned (bytecode size, proxy status, implementation), when to use it, error behavior, and pricing. Nothing essential for 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?

The single parameter 'address' is fully described in the schema, but the description adds a concrete example address and notes that a malformed address is rejected with 400, which provides extra semantic value beyond the schema's '0x address' label.

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 states a specific verb (check) and resource (0x address on Base), and enumerates the exact outputs: bytecode size, EIP-1167 proxy detection, and implementation address. It also distinguishes itself from the sibling check_counterparty for a fuller risk verdict.

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 explicit guidance: 'Use before sending funds or approving a spender; for a fuller risk verdict use check_counterparty.' This names the alternative and the condition that selects it, leaving nothing to inference.

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