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

With no annotations present, the description carries the full burden and does so thoroughly: unlisted counties collapse to RUS, Alaska/Hawaii return state areas, unknown codes and Connecticut planning regions return 404, territory codes return 404, and the Burlington County/military-site quirk is called out explicitly. These are exactly the non-obvious behaviors an agent cannot infer from schema or name.

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?

Purpose is front-loaded and the edge-case paragraph is dense with non-redundant information. It loses a point for the leading fragment 'GS locality pay area of a county,' which duplicates the sentence that follows (and appears to be a typo for GSA), plus the Burlington County detail, which is useful but disproportionate to a single county's military sites.

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?

There is no output schema, so the description must convey the return value, and it does: a locality pay area name, with `RUS` as the defined fallback and state areas for AK/HI. Complete for correct invocation and interpretation, though it never states the actual response shape (e.g., whether the area code and name are both returned).

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% and the schema already defines the five-digit FIPS pattern, so the baseline is 3. The description earns a notch above by adding semantic constraints the schema cannot express: which codes are rejected (Connecticut planning regions, territory codes) and a concrete example ('34005') whose behavior is spelled out.

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 opens with a specific verb and resource ('Return the locality pay area of a county') and pins the scope to 'the latest pay year, using OPM's own definitions.' Combined with the name, an agent can immediately distinguish this single-county lookup from the broader sibling get_opm_localities list without opening the 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 scope is clear enough to imply usage (per-county FIPS lookup), and the 404/fallback rules tell the agent a lot about edge conditions. But it never names an alternative — get_opm_localities, get_opm_pay, or search_opm_pay — or states when an agent should prefer one of those over this tool.

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