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

Annotations already cover read-only/idempotent/non-destructive behavior, and the description adds substantial context beyond them: fail-closed semantics, verdict values, safe_to outcomes, risk reasons, x402 pricing, and not_checked fields. It also states the per-call price and gives a sample call, leaving little behavioral ambiguity.

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 purpose is front-loaded in the first sentence and the rest is dense with operational details rather than filler. It is longer than typical because it enumerates returns without an output schema, but the structure remains readable and mostly earns its length.

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?

There is no output schema, so the description must explain return values, and it does so in detail: verdict, risk_score, safe_to flags, actions, reasons, domain_age_days, robots, http, x402, bot_policy, and not_checked. Combined with fail-closed guidance and a sample call, it is complete enough for an agent to invoke and interpret.

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% and both parameters are already described in the input schema. The description reinforces that UA affects robots.txt and bot policy, but adds little parameter-specific meaning beyond what the schema provides, so baseline 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 states a specific verb and resource: check whether a URL is safe to fetch, read, sign in to, or pay. It clearly distinguishes this pre-flight risk assessment from sibling tools like read_url or site_status by emphasizing a single safety verdict before proceeding.

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?

It gives clear usage context: call before fetching/reading/signing in/paying, and explicitly says fails closed so 'unknown' means do not proceed. It does not name alternative sibling tools or exclusion cases, so it stops 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.