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

Annotations already declare read-only, non-destructive, idempotent, open-world, so the safety profile is covered; the description adds genuinely new operational context: 8 s timeout, 5 redirect cap, 768 KiB body cap that applies only to GET, and a filtered header allowlist. It does not say how failures, blocked hosts, or non-2xx statuses surface, which keeps it below a 5.

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?

Four front-loaded sentences with no filler; the behavioral limits are condensed into a compact trailing clause. The telegraphic 'Limit: 8 s, 5 redirects, 768 KiB only for GET' is efficient but slightly clipped.

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?

An output schema exists, so return-value detail is not needed, and the limits plus method guidance cover the call mechanics. What is missing is error/failure behavior and whether redirect targets are re-validated against the public-URL rule, which matters for an open-world fetcher.

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?

With 50% schema coverage, the description carries real weight: it explains the semantics of the undocumented 'method' enum (HEAD = cheap check, GET = fallback for HEAD-hostile servers) and ties the 768 KiB limit to GET only. The 'url' parameter's constraint (no embedded credentials, public) is left to 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?

States a specific verb+resource ('Resolves a public URL through bounded redirects') and what is returned ('status plus a safe allowlist of HTTP headers'). It also names the sibling it is not ('Use extract_metadata for HTML semantic metadata'), so an agent can route without opening another schema.

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 explicit method selection rules — HEAD for cheap reachability/type checks, GET when a server mishandles HEAD — and names an alternative sibling for a different job. Both the when and the when-not are present.

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