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

Annotations already cover the safety profile (readOnlyHint=true, openWorldHint=false), yet the description still adds real value by naming the threat categories screened for and enumerating the four verdict outcomes with an accompanying reason. It does not disclose failure modes such as what happens if the reputation service is unreachable, which keeps it from a 5.

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?

Two sentences, front-loaded with the core check and followed by the return contract. No filler, no repetition of the schema, and the verdict vocabulary is stated compactly.

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 correctly carries the return-value burden by naming all four verdicts and the accompanying reason. For a two-parameter read-only tool that is close to sufficient; only the unknown/error-path behavior is left unstated.

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%, including the api_key note about raising the daily limit from 25 to 250, so the parameters are fully self-documenting in the schema. The description adds no additional meaning about the url format, canonicalization, or whether redirects are followed, so it sits at the 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 uses a specific verb plus resource and enumerates exactly what is being checked (prompt injection, data theft, destructive commands, payment fraud, phishing/malware lists), which is far beyond a tautology. It falls short of a 5 because it never distinguishes itself from close siblings such as check_urls or check_site, leaving the agent to infer that this one handles a single URL.

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 only implied: the title says 'before opening it' and the url parameter says 'you are about to open', which conveys a pre-flight check context. There is no explicit statement of when not to use it, nor any pointer to check_urls for batches or fetch_safely for the retrieval step, so routing between siblings stays guesswork.

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