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

With only readOnlyHint given, the description carries real behavioral weight: it discloses that the tool performs live outbound requests, rejects private/loopback/link-local/metadata and own hosts, bills 2 credits per successful call, and does not bill schema-invalid input. That is exactly the kind of cost, safety and eligibility context annotations cannot express.

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?

Front-loads the behavior in the first sentence, then gives return shape and price compactly. Dense but every clause earns its place; the result-shape literal is slightly heavy but useful given no output schema.

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 no output schema, the description supplies the exact return object (url, finalUrl, origin, status, preflight, headers, allowed, issues), plus pricing and refusal behavior. An agent has everything needed to call it and interpret the result.

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 description coverage is 100%, so all five parameters are already well documented, including the preflight triggers. The description restates the preflight rule at a high level but adds no format, default or edge-case meaning beyond the schema, which is the expected baseline.

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 and resource: sends a GET with an Origin header (plus an OPTIONS preflight when needed) and reports Access-Control-* headers with an allowed/blocked verdict. This is clearly distinguishable from nearby siblings like header-audit, http-status or curl-to-code without opening any 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?

The description makes the usage context clear: it emulates a browser cross-origin call and returns an allowed/blocked verdict, and it explains that non-simple methods, custom headers or credentials trigger a preflight. It does not name when to prefer a sibling such as header-audit or http-status, so no explicit exclusions are given.

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