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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely new behavior: a single outbound GET against the home page, a scope caveat that per-page policy may differ, and an explicit billing model (USDC per successful call via x402, failures not charged). The pricing disclosure is high-value context an agent cannot get from structured fields.

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?

Three sentences, front-loaded with the read-and-rate action and tightly packed with scope, output vocabulary and cost. The payment detail is dense but load-bearing for an agent that must decide whether to spend money.

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, the description need not explain return values, and it covers mechanism, scope limits, and cost. The only gap is that it never names a sibling for broader header auditing, which would complete the decision context.

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 with 100% schema description coverage, so the schema already explains 'domain'. The description implies the input is a site/domain and that a home page is fetched, but adds no format guidance (scheme handling, subdomains) beyond the schema.

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?

A specific verb set (reads the header and meta tag, computes the browser-effective policy, rates it strict/moderate/leaky) applied to a specific resource. The stated output vocabulary distinguishes it from a generic header scanner like security_security_headers.

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?

Scope context is supplied ('from the home page', 'one GET; links on other pages can set their own policy'), which tells the agent the audit is home-page-only. However, there is no explicit routing versus sibling tools such as security_security_headers or security_csp_evaluator_audit, so the agent must infer when this tool is the right pick.

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