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

Adds concrete behavior not covered by annotations: exactly one request, HEAD/GET choice, redirects are reported rather than followed, private and local addresses are refused (SSRF guard), and it never pays. These are operationally significant constraints an agent could not infer from readOnlyHint/idempotentHint alone.

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 tight sentences, front-loaded with the action and the reported output, then the safety constraints. No filler or repetition of the title.

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 values need no further explanation, and the description still summarizes what is reported. For a two-parameter probe with full annotation and schema coverage, nothing an agent needs to call it correctly is missing.

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% and both parameters are documented there (url as absolute http(s), method defaulting to GET), so the schema does the heavy lifting. The description only echoes the GET/HEAD choice without adding format or default nuance beyond 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 concrete operation ("Make one GET (or HEAD) request to a public URL") plus exactly what it returns: 402 presence, scheme, and decoded terms. An agent can distinguish this probing tool from siblings like decode_402_challenge or get_scheme_reference 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?

Usage is implied by "probe a public URL for 402 support," but the description never names an alternative or states when to prefer this over decode_402_challenge or get_best_payment_solution. Acceptable context, but routing between siblings is left to inference.

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