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

Annotations already declare readOnly/idempotent/non-destructive and open-world, so the safety profile is covered. The description adds real behavioral value beyond that: it names the underlying protocol (RDAP) and, importantly, discloses the failure mode for ccTLDs without RDAP — the tool reports the absence rather than fabricating an expiry, which directly shapes how an agent should interpret results.

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?

Two tight sentences, correctly front-loaded with what the tool does, followed by the one caveat that changes interpretation of results. No filler.

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 lookup with no output schema and annotations covering the safety profile, the description covers the essentials plus the notable RDAP gap. It stops short of describing what a successful response contains (expiry date, registrar, status), which would fully close the loop.

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?

Only one parameter and schema coverage is 100%, so the schema already explains that a full http(s) URL or a bare hostname (https assumed) is accepted. The description adds nothing about the input format, so the baseline 3 applies.

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 resource (domain registration) and data source (RDAP), making it clearly about domain expiry rather than page/URL checks. It never names a sibling such as stillindexed_check_url or stillindexed_check_tls, so an agent must infer the boundary from the resource noun alone.

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 the scope ('domain registration expiry'), but there is no explicit when-to-use statement, no mention of when a sibling is preferable, and no prerequisites. The ccTLD caveat is informative about outcomes, not about when to pick this tool.

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