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

Goes well beyond the annotations (which already cover read-only/idempotent/open-world) by disclosing the pricing model ($0.001/call, 10 free/day, x402 payment-required result), the error contract (isError with a message for invalid input or upstream failure, uncharged), and the specific diagnostic flags it raises (missing og:image, missing description, non-absolute image URLs).

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-loads the resource contents, then usage, then pricing/errors, with no filler sentences. It is on the long side for a one-parameter tool, but every clause (flags, price, error behavior) carries information an agent would otherwise lack.

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 an output schema present, return values need not be explained, and the description still covers routing, cost, error handling, and the problem-detection behavior. An agent has everything needed to call this correctly and interpret a failure.

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?

The single url parameter is fully documented in the schema ('Absolute http(s) URL of the page') at 100% coverage, and the description's statement that it operates on 'a page' is consistent but adds no new constraint or format detail. Baseline 3 is appropriate when the schema carries the parameter semantics.

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 concrete resource and enumerates exactly what it returns: title, description, OpenGraph/Twitter card, canonical, favicon, language, feeds, JSON-LD, headings, plus link-preview problem flags. It also explicitly separates itself from the nearest sibling ('for the article text use web_read').

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?

Names the concrete use cases (link previews, SEO/social card checks, feed/structured-data discovery) and gives an explicit routing rule versus web_read. Nothing about when to pick this tool is left to inference.

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