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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorldHint=false, so safety is covered. The description goes beyond that by disclosing the returned content, including 'data caveats', which is useful operational context an agent would not infer from the annotations. It does not cover pagination or response shape, keeping it short of a 5.

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. The returned-field list is front-loaded in sentence one and the usage trigger in sentence two, so both an invocation decision and a selection decision are supported immediately.

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 present, the description carries the burden of describing returns, and it does so by naming the exact per-world fields including the caveat field. For a parameterless, read-only listing tool this is sufficient for an agent to call and interpret it correctly.

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?

The tool takes zero parameters, so the baseline is 4: there is no parameter semantics for the description to add, and the description correctly implies a no-argument call.

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?

Specific verb (list) plus a concrete resource (worlds currently offered) and an enumeration of the fields returned: size, known places count, default relief, smallest selection, data caveats. That field set is unique among its siblings, so an agent can tell list_worlds apart from get_preview, get_product_info, or search_places without opening a 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 second sentence gives an explicit trigger: 'Use it when the user asks which planets or moons can be printed.' That is a clear usage context, but it names no exclusion or explicit alternative tool for adjacent requests (e.g. when the agent should call search_places or get_product_info instead).

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