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

Annotations already cover read-only, idempotent, open-world and non-destructive, so the description rightly spends its words elsewhere: it discloses that a remote fetch happens, exactly which validations are performed, and the cost/quota model (10 calls/day free, then $0.002 via HTTP endpoint or X-API-Key credits). It does not say how fetch failures, redirects or non-HTML pages are handled.

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?

Two compact sentences: the purpose question is front-loaded, then the checks, then pricing. The pricing sentence is on the long side but is genuine call-time information, so nothing is clearly wasted.

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, the description need not explain return values, so the remaining burden is scope, checks and cost — all covered. The gap is the edge case where neither url nor image is supplied, which is undefined here and only weakly implied by the schema.

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?

Schema coverage is 100% and both parameters are optional, so the schema carries parameter meaning; the description adds nothing about the 'url vs image' choice. In particular it does not clarify the mutually-exclusive/priority relationship that the schema only hints at with 'or an image URL directly'.

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 resource (the page's og:image) and a specific check set (status, type, file size, pixel dimensions, aspect ratio against 1200x630). It is clearly distinguishable from generic siblings like url_metadata, though it never names an alternative.

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 framing question ('Does the page's og:image work in link previews?') implies the use case well, but there is no explicit when-to-use/when-not guidance and no mention of the nearest alternative (url_metadata, http_inspect) for agents deciding between them.

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