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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description goes beyond them by disclosing the return shape: per-header findings plus fix advice, a score and a letter grade. It does not mention failure modes (unreachable hosts, non-HTTP schemes) or rate limits, 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?

Two tight sentences: the first states what the tool does and what it returns, the second handles routing. No filler, and the scope ('one URL') is front-loaded before the alternative is mentioned.

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 carries the burden of explaining returns and does so adequately (findings, fix advice, score, grade). For a single-URL read-only audit the coverage is nearly complete, though it omits error/edge-case behavior for invalid or non-responsive URLs.

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?

There is a single required parameter and schema coverage is 100%, so the schema already documents the url field adequately. The description only reiterates 'one URL' without adding format, scheme or scope constraints beyond what the schema states, 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?

The description opens with a specific verb and resource ('Audits the HTTP security headers of one URL') and enumerates the header families covered (CSP, HSTS, X-Frame-Options, Permissions-Policy, cross-origin policies). It also explicitly distinguishes itself from the sibling security_scan, so an agent can pick between them without reading either schema.

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 a direct usage condition ('Use it when you need header hardening advice') and names the alternative tool plus the reason to prefer it ('security_scan runs this audit together with URL reputation and subdomain discovery in one call'). This is explicit when-to-use and when-to-use-something-else guidance.

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