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

Annotations already establish readOnlyHint and openWorldHint, and the description adds genuinely new behavior: the fetch is passive (no active probing), billing is x402-based, and no charge applies when the host cannot be checked. It stops short of latency, rate limits, or failure modes.

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-loads purpose and scope, then layers return values, use cases, and billing in dense sentences with no filler. The flag enumeration is long but each item is informative, and no sentence is redundant.

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 still specifies the return values (verdict categories, score range, flag list) and covers the cost model and the no-charge edge case. Nothing an agent needs to invoke this correctly is missing.

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% and the single parameter is fully documented as an absolute HTTP/HTTPS URL. The description only reinforces that it takes one URL rather than adding format, length, or validation detail, so the baseline 3 applies.

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 ('safety check for one URL') and immediately narrows scope to a single URL, which separates it from check_sites_batch and check_site_safety_pro. It also enumerates the exact output shape (verdict, 0-100 score, named flags), so an agent knows precisely what it gets.

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?

Gives concrete when-to-use contexts ('before visiting, linking to, buying from, or submitting data to an unfamiliar site') and routes to list_prices for pricing. It never explicitly contrasts with the _pro variant or the batch sibling, so the agent must infer selection from the 'one URL' scope alone.

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