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

Annotations already establish readOnly, idempotent, non-destructive. The description adds genuinely useful behavior beyond them: it returns a boolean and performs no network access, which matters because the tool name suggests a safety assessment it explicitly does not perform.

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?

Three tight sentences, front-loaded with the core action, then usage, then the most important caveat. No filler and nothing 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 single-parameter boolean validator with no output schema, the description supplies the return type and the key limitation (no visitation, no safety judgment), which is everything an agent needs to call and interpret it.

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 1 parameter and 100% schema description coverage, the schema already documents the url string and its scheme restriction. The description's "absolute HTTP or HTTPS URL syntax" largely restates that constraint rather than adding format or length guidance.

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 (check) and resource (absolute HTTP/HTTPS URL syntax), which cleanly separates it from the many is-*-safe siblings that validate other formats. The closing clause explicitly disclaims site-safety assessment, preventing the 'safe' in the name from being misread.

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?

"Use to screen links before display or storage" gives a concrete usage context, and "does not ... assess the site's safety" implicitly rules out a security-check interpretation. However, it does not name alternative tools or state when validation is unnecessary.

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