coverage_for

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

With no annotations, the description carries the full burden, and it does disclose one genuinely useful behavioral trait: untracked places are reported as 'not covered' rather than as zero, and absence of coverage is not evidence of absence of transit data. That is valuable output semantics beyond the schema, but nothing is said about read-only safety, permissions, or result shape.

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, both earning their place: the first front-loads scope, the second front-loads the interpretation caveat. No filler, no repetition of the schema.

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 simple two-parameter read tool with no output schema and no annotations, the description covers what is returned, the granularity options, and the crucial not-covered-vs-zero semantics. It stops short of saying whether the optional subdivision is required for subdivision-level output or what the totals are keyed on, but the gap is small.

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 description coverage is 100%, so both parameters (country as ISO 3166-1 alpha-2, subdivision as ISO 3166-2 code or name) are already fully documented. The description's 'one ISO country, or one subdivision inside it' only restates that relationship without adding format or edge-case detail, 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 ('Covered-set totals') and an explicit scope (one ISO country, or a subdivision inside it), which is concrete enough for an agent to know what comes back. It does not, however, contrast itself with the obviously related siblings coverage_stats or national_stats, so disambiguation must come from elsewhere.

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 scope phrasing implies the use case (single-country / single-subdivision lookups), but there is no explicit when-to-use statement and no named alternative such as coverage_stats or national_stats for aggregate or comparative queries. Usage is inferable rather than stated.

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