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

Annotations declare openWorldHint=true, readOnlyHint=false, and idempotentHint=false, and the description adds substantial context beyond them: the exact cost (0.01 USDC or 0.01 USD credit), the required wallet/header auth, and the requestId retry semantics that prevent a duplicate debit. It stops short of describing failure/refund behavior or what happens if the credit balance is insufficient, so it is strong but not exhaustive.

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?

Payment and auth conditions are front-loaded and the output ("recommendation and alternatives") and boundary ("supplier purchase is separate") are stated compactly. The clause stacking is dense but each sentence contributes information; there is little filler.

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 does supply the return shape (recommendation plus alternatives), payment model, auth requirements, and the retry/idempotency contract. The main gap is that the country and language parameters affecting comparison are left unexplained, which matters for a geographically scoped comparison tool.

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 description coverage is only 25%, so the description carries added burden; it does explain requestId well (fresh UUID per task, reused only for identical retries) and ties it to the credit payment path. But country and language are never mentioned, and intent is only indirectly conveyed through "buyer task."

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?

"Compare APIs for a buyer task" gives a specific verb (compare) and resource (APIs) scoped to a buyer use case, which separates it from sibling listing/lookup tools like via_list_services. It does not explicitly contrast with via_one_call or via_one_call_quote, the closest competing buyer tools, so the distinction is inferable rather than stated.

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?

The description does explain the two payment paths (x402 USDC on Base vs prepaid VIA credit with an x-credit-token header) and that supplier purchase is a separate step, which implies this is a pre-purchase comparison step. However, it never states when to choose this over via_one_call, via_one_call_quote, or via_list_services, so selection guidance is implied rather than explicit.

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