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

Annotations only give readOnlyHint and openWorldHint; the description adds material context beyond them: a per-call price, a free-on-unreachable pricing exception, an explicit epistemic caveat ('Heuristic, not a guarantee'), and the assurance that the scan does not itself authorize payment. These are exactly the traits an agent needs before spending money on a scan.

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?

Three sentences, all load-bearing, with the scope constraint and price front-loaded before the sibling routing. The first sentence is a heavy enumeration, but each listed check maps to a real capability rather than padding.

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?

Output shape is covered by the output schema, so the description only needs to convey purpose, cost, limits, and alternatives — all present. An agent can decide, pay for, and interpret this call without opening anything else.

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 100%, so target_url and context are already documented in the schema, and the description adds no syntax, format, or constraint detail beyond them. Baseline 3 applies because the schema carries the parameter burden.

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 and resource ('Pre-payment check of an x402 API endpoint') and enumerates exactly what is inspected: discovery files, live 402 terms, USDC prices, latency, prompt-injection flags, and CDP Bazaar statistics. It explicitly distinguishes itself from the closest sibling by routing online shops to pre_purchase_merchant_trust_check.

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?

Usage is anchored to a concrete decision point ('before signing a payment authorization'), with an explicit alternative named for the adjacent use case ('Online shops: pre_purchase_merchant_trust_check'). The cost/refund rule ('$0.002; unreachable targets are free') further informs the call decision.

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