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

Annotations already declare readOnlyHint=true, openWorldHint=true, destructiveHint=false, so safety and network reach are covered. The description still adds real behavioral value: it discloses that output includes derived "findings for anything missing or too long," i.e. a verdict rather than raw HTML, which the annotations cannot convey. It does not mention failure modes (unreachable URLs, non-HTML responses, timeouts), which would have earned 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?

A single sentence, front-loaded with the verb and the inspecting-subject ("what crawlers and link unfurlers see"), followed by a compact enumeration. The long list is justified because there is no output schema, so it is disclosure rather than padding. Slightly dense but zero filler sentences.

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 correctly compensates by enumerating the return contents, including the computed preview card and findings. What is missing for a network-fetching tool is error/boundary behavior (timeouts, non-HTML, redirects) and the sibling routing decision, keeping it short of a 5.

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?

One parameter with 100% schema description coverage ("The page to fetch"), so the schema does the work; baseline 3 applies. The description adds no URL format, redirect, or scheme guidance beyond what the schema already says.

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 concrete verb+resource ("Fetch a URL and report") and enumerates exactly what is inspected: title, meta description lengths, canonical, lang, viewport, robots meta, h1s, OG/Twitter tags, favicon, JSON-LD, preview card, findings. Purpose is unmistakable, but there is no differentiation from siblings that also fetch and inspect a URL (check_headers, check_ai_crawlers, check_tells), so an agent must guess which checker applies.

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?

There is no when-to-use statement and no named alternative. With three sibling tools that also take a URL and inspect a page (check_headers, check_ai_crawlers, check_tells), the description should say which concern it owns (SEO/social metadata vs headers vs crawler policy). The enumerated outputs imply the domain but never route the agent.

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