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

The description discloses the return contract (reasons + GO/HOLD/STOP verdict), the pricing model ($0.002/call over x402 on Base), the auth mechanism (prepaid x-credit-token header for unlimited calls, 1 free call/day, no API key). Annotations only cover read-only/idempotent/open-world safety, so this adds substantial operational context the agent cannot get elsewhere.

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?

Front-loaded with the core purpose and heuristics before moving to caveats, output, and pricing. Dense but every sentence carries information; the pricing/auth sentence is long but necessary given no annotations cover it.

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?

Covers purpose, scope exclusions, verdict output, cost, and auth. An output schema exists so return-value detail is unnecessary, and the description supplies everything else an agent needs to decide and invoke correctly.

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 baseline is 3. The description adds value by clarifying the optional brand parameter's purpose as a lookalike comparison ('optional brand= lookalike') and confirms url is the required input, going slightly beyond the schema's terse 'Expected brand host' wording.

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 ('Heuristic URL risk') and enumerates the exact dimensions analyzed (scheme, IP hosts, deep subdomains, credential-themed labels, sensitive paths/params, brand lookalike). This clearly distinguishes it from siblings like url_extract, url_to_json, or ssl_check, which have different outputs.

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 you click' frames the workflow position, and 'Not a malware or Safe Browsing scan' draws an explicit boundary excluding adjacent use cases. It also states the required input. What's missing is naming a concrete alternative tool for those excluded cases, so it is not a full 5.

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