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

With no annotations, the description carries the full burden and discloses the core behavior: blocklist plus live heuristics (redirect chain, host reputation, lookalike patterns), the return of a verdict with rules that fired, and the payment mechanism. It lacks details on rate limits or edge-case behavior, but it is substantial for a screening tool.

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 two sentences with no fluff. The first sentence packs purpose, method, and return value; the second focuses on payment. It is slightly dense but appropriately sized for the tool's complexity.

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 tool has 3 params and no output schema, the description covers the return value ('verdict with the rules that fired') and the payment workflow, which are the critical contextual gaps. It does not discuss error handling or edge cases, but for this level of complexity, it is sufficiently complete.

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 the baseline is 3. The description adds significant meaning to the x_payment parameter by explaining the two-step payment flow (omit to receive terms, sign, call again with x_payment). It does not add extra semantics for 'url' or 'follow', but the x_payment context pushes this above baseline.

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 clearly states the tool's function with a specific verb ('Screen'), a specific resource ('a URL'), and a specific method ('against the URLhaus blocklist snapshot plus deterministic live heuristics'). It also distinguishes this tool from siblings like address_screen or domain_intel by focusing on phishing/malicious URL screening.

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 provides explicit usage context, including the payment workflow (call without x_payment to get terms, sign, then call again with x_payment) and references the pricing tool as an alternative for price information. However, it does not explicitly exclude sibling tools for other intelligence types, so it falls short of a 5.

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