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

Annotations only say readOnlyHint=false, idempotentHint=false, destructiveHint=false. The description goes well beyond them: a firewall/rate limit returns 502 target_blocked rather than a score, exhaustion returns 402 with accepts[] and code allowance_spent, there is no captcha, and repeats are allowed after payment. That is exactly the operational detail an agent needs and none of it is in the 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?

Front-loaded with the audit scope, then behavioral/payment semantics. Nearly every sentence carries actionable information, though 'This is the product for agents' and the captcha remark lean slightly promotional and could be trimmed without loss.

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?

No output schema exists, so the description must carry return semantics; it states it 'Returns evidence, limits and fixes without a tab' and fully specifies the two error paths (502 target_blocked, 402 accepts[]). It could be slightly fuller on the shape of the evidence payload, but it is sufficient to call the tool correctly.

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%, so the schema already documents 'url' (absolute URL) and 'guest_token' (optional pa_…). The description adds no syntax, format, or constraint detail for either parameter, so it earns only the baseline 3.

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 gives a highly specific verb+resource ('Audits a URL') and enumerates exactly what is audited (SEO/meta, canonical, JSON-LD, robots.txt per crawler, CWV, llms.txt, security.txt, favicon). It also scopes it ('not a security/accessibility certification'). However, it never distinguishes itself from the obvious sibling get_audit (run vs. retrieve results), so it stops short of a 5.

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 when-to-use context: 'This is the product for agents', and positions the free path as 'a person signs in with an account to get the trial', plus what to do when the allowance is exhausted (pay and repeat the same call). Clear context, but no explicit statement of when to prefer a sibling such as get_audit or run_tab.

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