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

With no annotations, the description carries the full burden and does useful work: it discloses the free-tier quota (3 URL scans/day/IP), the Pro escape hatch via a license email, and the shape of the result (score, findings, shareable report URL). It stops short of stating the operation is read-only/side-effect free or how rendering failures/timeouts behave.

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 tight sentences, front-loaded with what the tool does and immediately followed by the return contract and the quota constraint. No filler or redundant restatement of the name.

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?

For a four-parameter, no-annotation tool with no output schema, the description supplies the return contents (score, findings, report URL), quota limits, and licensing. It omits the read-only/safety profile and any failure-mode behavior, which is the main remaining gap.

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 all four parameters are already documented, including the mobile/desktop viewport enum and the site crawl limit. The description's quota mention overlaps rather than extends the schema's 'crawl same-origin pages (3 free / 10 Pro)' note, so the baseline of 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 gives a specific verb pair (render and audit), a precise resource (a live web page), and the standard applied (WCAG 2.1/2.2). The word 'live' implicitly separates it from the sibling scan_html, so an agent can route between them without opening a 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?

Usage is only implied: audit a live URL. It never states when to prefer scan_url over scan_html (static markup) or when get_report should be used instead, and the rate-limit note describes cost rather than selection criteria.

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