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

Beyond the readOnly/destructive annotations it discloses pricing ($0.01/call via x402, first 25 free, failed calls free), error semantics (404 for missing contract, 422 for non-ERC-20, both uncharged), and clarifies that repeats are billed — directly explaining the idempotentHint=false flag in practical terms.

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 is front-loaded and every sentence carries information, but the pricing/billing clauses are packed into a dense multi-clause sentence that could be trimmed or split without losing meaning.

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?

Only three fully-specified parameters, no output schema, and the description still covers the return shape, error behavior, cost model, and a sibling alternative — nothing an agent needs in order to call it correctly 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?

Schema coverage is 100%, so the baseline is 3; the description adds meaning beyond the schema by explaining that the token parameter accepts a ticker or 0x contract and what each failure mode (404/422) maps to. Owner and spender semantics are largely restated from the schema, so not a 5.

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+resource: ERC-20 allowance on Optimism, plus what is returned (raw and token units, unlimited flag). It explicitly distinguishes itself from the sibling op_token_balance, so an agent can separate the two without opening schemas.

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 concrete when-to-use cases ('check an approval before a swap or to audit risky open approvals') and names the alternative for a different need ('for the owner's balance use op_token_balance'). Routing is unambiguous.

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