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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the bar is lower; the description still adds real behavior: a hard 25-domain batch cap, a "pending" state for timeouts, and the fact that pending entries are re-checkable. It stops short of saying whether results are cached or rate-limited.

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 sentences, zero filler, and the highest-value facts (batch cap, returned fields, sort order) come first, with the timeout caveat and no-account note trailing.

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?

Absent an output schema, the description carries the return-value burden and does so by naming the three result fields plus the sort order and the timeout sentinel. Minor gaps remain around invalid-domain handling and the pending re-check mechanics.

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 a single parameter at 100% schema coverage, the schema already documents the 1-25 array bounds via minItems/maxItems and its own description. The description's "up to 25 domains at once" merely restates that constraint rather than adding format guidance such as accepted domain syntax or TLD handling.

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?

The description names a concrete verb and resource ("Checks up to 25 domains at once") and enumerates the returned fields (expiry date, days left, registrar), which lets an agent separate it from lookup_domain and check_ssl_certificate 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?

"Does not need a TLDix account" tells the agent this works without authentication, distinguishing it from the account-bound siblings like list_tracked_domains and list_upcoming_renewals. It also covers the retry path for timed-out domains, but never explicitly says when to prefer lookup_domain or the tracked-domain tools instead.

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