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

With no annotations, the description must carry the behavioral burden, and it does disclose two useful things: the returned fields and a 1-credit cost. It does not say whether the tool is read-only, how failures surface (false vs. error), timeouts, redirect handling, or whether it verifies certificate validity versus merely completing a handshake.

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?

One front-loaded sentence with the returned fields, plus a parenthetical cost note. No filler, nothing repeated, and the most decision-relevant content comes first.

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 read-only check with no output schema, listing the response fields covers most of what an agent needs. It is still thin on the meaning of a negative result and on the fact that the parameter is effectively required despite the schema marking zero required fields.

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%, so the baseline is 3, but the schema's own text ('string, required') is tautological rather than informative. The description adds only the word 'domain', implying a bare hostname rather than a full URL — mildly useful but not enough to rise above 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 check — whether a domain answers over HTTPS — and enumerates the returned fields (status, server, HSTS headers), which separates it from siblings like rdap_lookup or unshorten. It never explicitly names those siblings, so an agent must infer the boundary itself.

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?

There is no when-to-use guidance at all: nothing says to prefer this over rdap_lookup for domain questions or over unshorten for URL resolution, and no prerequisites (publicly reachable domain, DNS requirement) are stated. The only contextual cue is the credit cost, which is about budgeting, not selection.

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