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

Adds substantial context beyond the annotations: 1 MB read cap, no JavaScript execution, no mutations, per-call pricing ($0.01 via x402/card key), first 25 free, failed calls free, and repeats are billed. That pricing detail also explains the idempotentHint=false annotation (repeat calls cost money) rather than contradicting it.

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 behavior and returned fields, then usage, then cost. Mostly tight, though the trailing 'reads or computes only and changes nothing' partially restates the annotations and the charged-per-call point is repeated.

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, yet the description lists the return fields in detail, and with a single fully documented parameter plus rich annotations, an agent has everything needed to call this correctly.

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?

Only one parameter, and the schema already documents it at 100% coverage (absolute public http(s) URL). The description reinforces the 'public' constraint and supplies a concrete example URL, adding modest value 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?

Names a specific verb and resource (fetch a public web page's head, return link-preview metadata) and enumerates the returned fields. Clearly distinct from siblings like extract, extract_rendered, or url_favicon, which do different jobs.

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?

Gives three concrete use cases (build link previews, label citations, preview how a URL unfurls) and an example call. It does not, however, say when to prefer a sibling such as extract or seo_audit, so the routing decision is left implicit.

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