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

With no annotations, the description carries the disclosure burden and does it well: it defines the destination abstraction, explains the ID 0 fallback, gives the default-date behavior, and states exactly what the response contains (seasonal lodging rate plus M&IE rate). Auth requirements, error behavior, and whether historical dates are supported are not mentioned.

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?

Well front-loaded: the core action is the first sentence and the destination/ID caveats follow in logical order. The leading bare line "GSA per diem rate by destination" duplicates the title and the next sentence, costing a little tightness.

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 takes on return-value disclosure and does so precisely (lodging rate for the date, M&IE rate, optional verification URL). For a single-record read lookup, everything an agent needs to invoke it correctly is present.

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 already 100%, so the baseline is 3; the description still adds genuine meaning beyond it — the semantic nature of `destination_id` (a GSA rate area that may span a county or the whole CONUS area) and the default behavior for an omitted `date`, which the schema does not state.

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 verb and resource ("Return the GSA per diem rate") scoped by destination and date, and immediately clarifies that a destination is a GSA rate area rather than a municipality. This distinguishes it from siblings like get_gsa_perdiem_by_zipcode, get_gsa_perdiem_by_state, and get_destinations without needing 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?

Explicitly routes the agent to `GET /v1/gsa/destinations` to resolve a destination ID, and states that ID 0 means Standard CONUS and that omitting `date` returns today's rate. It does not, however, say when to prefer this tool over the by-zipcode or by-state variants, so the sibling selection is only partially covered.

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