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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the description's job is to add what they can't. It does: free tier of 10 calls/day, then $0.002 via the HTTP endpoint or X-API-Key credits, which is exactly the kind of cost/rate-limit constraint an agent needs before calling. It also discloses the output boundary (metadata only). It does not mention failure modes for unreachable or non-HTML URLs, but the additions are substantive.

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?

The returned fields are front-loaded in the first sentence, with scope and pricing after. The field enumeration is long but each item is a distinct output category, so it earns its space. No filler or restated title.

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?

This is a low-complexity, single-parameter read tool with an output schema, so return-value documentation is unnecessary and the description correctly skips it. Between the field list, the content exclusion, and the pricing model, an agent has what it needs to call it correctly. The only real gap is sibling disambiguation against og_image_check and http_inspect.

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?

There is a single required parameter with 100% schema description coverage, so the schema carries the semantics and the baseline is 3. The description adds nothing about the url parameter (no accepted formats, redirect handling, or whether non-HTML URLs are valid), leaving the schema to do all the work.

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 names a specific resource and enumerates exactly what is extracted (title, description, canonical, language, favicon, OG/Twitter cards, JSON-LD types, feeds, word count), plus a clear scope boundary: 'Metadata only, not page content.' That is far more than a restatement of the name. It stops short of differentiating from the nearest siblings, notably og_image_check (also link-preview oriented) and http_inspect, so an agent still has to infer which of those to pick.

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 implied rather than stated: fetch metadata for a page URL, and explicitly not page content. There is no when-to-use/when-not-to-use framing and no mention of the sibling tools (og_image_check, http_inspect, url_parse_clean) that an agent could confuse this with. The 'not page content' line is a useful scope exclusion but is the only routing signal.

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