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

Annotations already cover read-only and open-world safety, but the description adds real behavioral context: HEAD (no body fetch, lightweight), redirects are followed so the returned status is the final one, and the target must be a public URL. It stops short of saying what happens on unreachable hosts or whether it returns an error vs partial data.

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?

A single sentence that front-loads the returned resource and uses the parenthetical for the method and redirect behavior. Nothing is wasted or buried.

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?

For a one-parameter read tool with no output schema, the description adequately covers what is retrieved and how. The remaining gaps — error behavior on unreachable hosts and the shape of the returned headers — are minor, though the latter would help since no output schema exists.

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 there is only one parameter, so the schema already carries the burden. The description adds the 'public' restriction, which is a meaningful constraint beyond the schema's 'URL or domain' example, but little else.

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 (HTTP response headers and status) and the method used (HEAD request), which is clearly distinct from siblings like dns_lookup, ssl_check, and whois. It never explicitly names an alternative, but the resource boundary is unambiguous.

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 only implied: 'public URL' hints at a precondition (internal/private hosts presumably unsupported) and the resource implies you call it when you need status/header info. There is no explicit statement of when to prefer this over ssl_check or dns_lookup for a URL's health.

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