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

Annotations already declare this is a safe read (readOnlyHint) against an open world. The description adds genuinely useful behavior the annotations don't cover: it is a paid call costing $0.002 USDC via x402, which is critical for an agent deciding whether to invoke it. It omits any note on failures/timeouts or rate limits, keeping it out of 5 territory.

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 core purpose in the first clause, then spends the rest on the returned field list and the price. The field enumeration is long but earns its place given there is no output schema to document the return shape.

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 usefully enumerates what comes back (title, description, image, oEmbed, schema.org types, etc.) and discloses the per-call cost. It is close to complete for a one-parameter read tool, missing only input format and error behavior.

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 has 0% schema description coverage, so the description carries the full burden. "for any URL" weakly signals that no domain restriction applies, but says nothing about accepted formats (scheme, encoding, redirects), which is thin for the one input that matters.

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?

Names a specific verb and resource ("Link preview data for any URL") and enumerates the returned fields, which effectively separates it from siblings like url_unshorten or scrape. It never explicitly names an alternative, so it stops short of a 5.

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?

The description gives no when-to-use vs when-not-to-use guidance and never points to a sibling such as url_unshorten, link, or scrape. "What chat apps show when you paste a link" describes the output's flavor, not the conditions under which an agent should pick this tool.

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