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

Annotations already establish readOnly, idempotent, non-destructive, open-world. The description adds real context beyond them: SSRF-safe fetching, an explicit cost ($0.01 USDC per successful call via x402/Solana), the fact that billing is per successful call, and an equivalent HTTPS endpoint. It stops short of failure/rate-limit behavior, which keeps it at 4.

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 core purpose, then a dense feature enumeration, then short operational sentences for SSRF safety, price, and the HTTP fallback. The feature list is long but every item is meaningful; no idle prose. The single 200-word first sentence is heavy but readable.

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, and the description compensates by describing the return shape (0-100 score, letter grade, prioritised high/medium/low issues) plus the audited surface. Combined with the pricing and transport details, an agent has everything needed to call it and interpret the result; only failure modes and latency expectations are absent.

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 both the url and robots parameters are already documented including the default. The description only obliquely reinforces the robots parameter by mentioning robots.txt allow/deny and declared sitemaps in the audit scope; it adds no format, validation, or edge-case semantics 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?

Opens with a specific verb+resource ("On-page SEO audit of one URL") and enumerates the exact checks it performs, so the agent knows precisely what class of work this is. It does not name which sibling to use instead of or alongside it (headers_audit, robots_sitemap, opengraph), so sibling differentiation is left implicit.

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 rather than stated: the breadth of the check list signals "use this for a full page-level audit" versus the single-purpose siblings, but there is no explicit when-to-use/when-not guidance or comparison to headers_audit or robots_sitemap. Nothing tells the agent when a narrower sibling would suffice.

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