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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so the safety profile is covered. The description adds that the service is "Free and public" (a cost/auth signal) and restates the default-level resolution, but says nothing about result shape, ordering, pagination, or what happens when a boundary has no children. Useful but thin beyond the structured fields.

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?

The concept and examples come first, followed by the default rule, then cost, then use cases - a sensible front-loaded order across four short sentences. The standalone "Free and public." fragment is terse but earns its place as a cost signal; otherwise near-zero waste.

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 only two parameters and rich annotations, the description covers concept, defaulting, and purpose. However, there is no output schema, so the description should say what a returned subdivision looks like (identifier format, name, admin_level) and whether an empty result is possible for a leaf boundary - an agent cannot infer that from anything supplied.

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 both the id formats and the admin_level range/default are already fully documented in the schema. The description's only parameter-relevant sentence repeats the default resolution rule already present in the admin_level field description, adding no new meaning. 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?

The description names the exact resource (the direct subdivisions of a boundary) and illustrates the hierarchy with concrete examples (country->states, state->counties, city->districts), so an agent knows precisely what comes back. It does not explicitly contrast itself with siblings like get_boundary, search_boundaries, or contains_points, leaving the distinction to inference from names.

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?

"Use it to build drill-down pickers or to cover a region with its parts" gives a concrete use context, and the admin_level default rule tells the agent it can call it without any level argument. There is no when-not guidance or explicit alternative (e.g. use get_boundary for the parent itself), which keeps it below a 5.

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