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

With no annotations, the description carries the full burden and does so well: default token (USDC), refusal of non-tokens before payment, per-call price ($0.001), the payment rail options, the two-step sign/pay protocol, and the 'never guessed' accuracy guarantee on spender names. These are material behavioral facts an agent cannot get from the schema.

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 purpose is front-loaded and every clause carries information, but the middle section is a dense run-on of comma-separated return fields that could be structured better. Overall efficient with little waste.

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?

For a paid read tool with no annotations and no output schema, the description covers the otherwise-missing return values, the pricing model, the refusal case, and the full payment protocol. An agent has everything needed to invoke it correctly across both phases.

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, but the description adds real meaning: it explains that `token` defaults to USDC, and more importantly it describes how `payment` drives the two-phase purchase flow (pass it and the call completes). That goes beyond the schema's one-line gloss.

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 opening clause names a specific verb and resource ('Allowance check on Arc before an approval') and then enumerates precisely what is returned: approval amount, unlimited flag, USD value, owner balance, spender identity, risk signals. The 'on Arc' scoping and explicit output list let an agent distinguish it from the generic `evm_allowance` sibling without opening either 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?

'before an approval' establishes the intended moment of use, and the closing sentences describe the exact two-step x402 flow (call without `payment` for terms, sign, call again with `payment`). It stops short of naming the alternative tool (`evm_allowance`) or stating when NOT to use it.

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