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

Annotations already cover the safe-read profile (readOnly, idempotent, non-destructive, openWorld), so credit goes to the added context: a per-call price of 0.02 USDC, the x402 payment rail with five supported chains, and the fact that 400/503 failures are not billed. That is real behavioral disclosure an agent needs before calling. It does not explain the payment handshake or auth flow, 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?

Four tight sentences: trigger, return payload, failure billing, price. The trigger is front-loaded and every sentence carries information an agent cannot get from schema or annotations. No filler.

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 an output schema present and 100% param coverage, the description needn't explain return shapes, and the cost/error behavior makes it safe to invoke. The remaining gap is sibling positioning — an agent choosing between this, get_domain, and get_web_markdown gets no help.

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 'url' parameter is fully documented in-schema (absolute https URL, standard port, host not IP). The description adds no constraint or format detail of its own, 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 resource ('technical facts of one website') and enumerates exactly what comes back: TLS certificate, DNS records, security-header grade over 8 checks, tech stack, social links. An agent immediately knows what it gets. It stops short of a 5 because it never distinguishes itself from close siblings like get_domain or get_web_markdown.

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?

'Use when an agent needs the technical facts of one website' is a genuine use-case trigger, but there is no explicit when-not, no prerequisite, and no named alternative for overlapping needs (e.g. get_domain, get_web_markdown). Usage is implied rather than routed.

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