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

Annotations already establish read-only, idempotent, closed-world, non-destructive behavior, so the description's burden is lighter. It still adds real value by disclosing that absent data is returned as null 'with their status' rather than omitted, which tells the agent how to interpret gaps. It does not describe result size or shape, but that is a minor omission given the annotation coverage.

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 short sentences with the identifier formats front-loaded and the null-handling note second. Nothing is repeated from the schema or annotations, and no sentence is wasted.

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, the description is the only source of return-value information, and 'all atlas values' is undefined vocabulary — the agent cannot tell which measures or what structure comes back. The null-with-status note partially fills that gap, but the response shape remains largely opaque for a lookup tool.

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 0% and the single parameter has no description, so the description must compensate, and it does: it names the accepted formats (5-digit FIPS, or "Name, State" where state is a name or postal code). Edge cases like case sensitivity, whitespace, or ambiguous county names are left unaddressed.

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 concrete resource and scope: 'All atlas values for one county', with the identifier forms it accepts. An agent can tell this is the single-county lookup versus compare_counties or rank_counties, though it never names those siblings explicitly.

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 ('one county') rather than stated: fetch everything known for a single county. There is no explicit when-not guidance and no routing to alternatives such as compare_counties for multi-county work or find_measure when the agent only needs one metric.

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