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

Beyond the annotations (readOnly, openWorld), the description discloses the return shape (monthly lodging breakdown for seasonal locations, M&IE), the three possible status outcomes with their meaning, and the CONUS-only limitation. These are exactly the behavioral facts an agent needs and none are restated from 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?

Front-loaded with the purpose, then organized param-by-param followed by status semantics. It is longer than average but nearly every line carries information; the status enumeration is slightly verbose but justified for a multi-outcome tool.

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 four-parameter, open-world lookup with ambiguous-resolution risk, the description covers edge cases (seasonal rates, ambiguity, unrecognized cities, non-CONUS) that an agent could not infer from the schema alone. An output schema exists so return-value detail is a bonus rather than a requirement.

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%, so the description carries the burden and largely succeeds: state format is specified (2-letter USPS code with examples), fiscal_year gets a default and a precise FY date range, and county gets examples plus its resolution behavior. Only 'city' lacks explicit format guidance, which is a minor gap given it is the primary argument.

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: looking up federal per diem rates for a city and state, and immediately names the returned artifacts (lodging, M&IE). The city+state scoping implicitly separates it from zip-based and state-level siblings, 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?

It gives clear operational context: county is optional and bypasses an API call when supplied for a bundled fiscal year, fiscal_year defaults to the current FY, and AK/HI/territories are out of scope with a pointer elsewhere. It does not, however, state when to prefer lookup_zip_perdiem or lookup_state_rates over this tool.

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