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

Goes far beyond the readOnlyHint/openWorldHint/idempotentHint annotations: it discloses the x402 payment requirement and price, the exact failure shape (isError plus structuredContent with x402Version 2 and accepts), the retry mechanism via params._meta["x402/payment"], and where settlement lands (result._meta["x402/payment-response"]). Billing semantics ('charged only if the page could be fetched') are exactly the kind of trait annotations cannot carry.

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 and result shape, then the payment mechanics — a sensible ordering with no filler sentences. The 15-item checklist is long but each item is a real check the agent may need to reason about; the redundant 'Send {url}' line is the only wasted fragment.

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 still specifies the return payload (0-100 score, grade, prioritized issues, JSON text) and the payment-response envelope. Payment, error, and success paths are all covered, so nothing an agent needs to invoke or recover is missing.

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 with 100% schema description coverage, so the schema already documents it fully. 'Send {url}' adds nothing beyond what the schema states, and the description doesn't clarify edge cases like non-public hosts or redirect targets. Baseline 3 is the correct ceiling here.

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 verb and resource ('technical and SEO audit of a public web page') and then enumerates exactly what is checked (HTTPS/redirect, status, title/meta, viewport, canonical, OG, alt text, structured data, headers). No sibling tool overlaps with page auditing, so no differentiation is needed.

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 is clear: a public page, one URL, and the billing condition ('charged only if the page could be fetched') tells the agent when cost is incurred. It also tells the agent what to do on the unpaid path (sign an accepts entry and retry), though it never states when *not* to use it — there is no real alternative among the siblings anyway.

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