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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds value by disclosing the underlying analysis sources (URLhaus + heuristic analysis) and the specific threat categories (malware, phishing, other threats), which provides behavioral context beyond the annotations.

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 concise sentences, front-loaded with the core action ('Check a URL...') and a short secondary sentence on methodology. No unnecessary words or repetition.

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 simple read-only tool with one parameter, the description covers purpose, method, and threat scope. There is no output schema, so the description could theoretically mention the return format, but the tool is simple enough that this omission is not a major gap.

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% with the 'url' parameter well-described ('The URL to check (e.g. https://example.com)'). The tool description adds minimal extra parameter meaning—it only repeats 'URL'—so a baseline score of 3 is appropriate.

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 action 'Check a URL' and the specific purpose 'for malware, phishing, and other threats'. This distinguishes it from sibling tools like check_domain, check_email, or check_ip by explicitly targeting URLs.

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 clearly sets the context by specifying a URL as the input type, and mentions the analysis method (URLhaus + heuristics). It does not explicitly name alternatives or state when not to use it, but the scope is clear enough for an agent to select this tool for URL checks.

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