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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds genuinely non-schema behavior: free quota of 10 calls/day, then $0.002/call, and the two payment mechanisms (x402 via params._meta or HTTP, or X-API-Key credits) — information an agent cannot get anywhere else. It stops short of describing latency, failure modes, or what counts as a billable call.

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?

A single dense sentence leads with the deliverable and its checks, then closes with cost and payment mechanics — front-loaded and free of filler. Every clause carries actionable information for an agent, including the billing path and the serving host.

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?

An output schema exists, so return-shape detail is unnecessary, and the single required parameter is fully documented. The description covers scope, cost and payment, which is what an agent needs to call it correctly; only edge-case behavior (invalid URLs, timeouts, non-HTML responses) is unaddressed.

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?

Only one parameter and schema coverage is 100%, with an example value and description already in the schema, so the baseline of 3 applies. The description implies the input is a page URL ('page URL' framing via the audited-header context) but adds no format requirements such as scheme handling or whether redirects are followed.

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?

Names a specific verb and resource ('Graded audit of HSTS, CSP, clickjacking, nosniff, ...') and enumerates the exact checks plus the A-F grading, so an agent knows precisely what it gets back. No sibling in the catalog overlaps this behavior, so differentiation is implicit but unambiguous.

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 implied (audit the security headers of a page URL) and the pricing/free-tier line helps an agent decide whether to spend a call, but there is no explicit 'use when / do not use when' guidance and no named alternative for adjacent checks. Adequate but leaves selection reasoning to inference.

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