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

Annotations already declare readOnly, idempotent, non-destructive, and non-open-world, so the safety profile is covered. The description goes well beyond that by disclosing effective-date windows (Oct. 1, 2026 onward vs. Oct. 1, 2025 – Sept. 30, 2026), the governing IRS notices, the transportation-industry M&IE rates, the $5 incidental-only rate, and the size of the high-cost locality list including seasonal portions.

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?

The purpose is front-loaded in the first clause, which is good, but the remainder is a dense run-on of dollar figures, notice numbers, and parenthetical asides. The rate values and Notice citations are plausibly useful for answering without follow-up calls, but the packing hurts scanability and buries the high-cost-locality check mid-sentence.

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 carries the burden of describing returns, and it does: rate pairs, meal components, transportation M&IE, incidental rate, and a high-cost locality determination with seasonal variants. Gaps remain around behavior for unmatched cities, missing state, or dates outside the published windows, and around response shape, but the substantive business content is there.

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 the schema already documents city, date, and state, including the YYYY-MM-DD pattern and the today-default. The description adds only indirect meaning ('for a date', 'whether a city is a high-cost locality') and never mentions the state parameter or how city+state combine for locality matching, 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?

The description states a specific verb and resource: it returns IRS high-low substantiation rates for a date and a boolean-ish answer on whether a city is a high-cost locality. The 'high-low substantiation method' phrasing implicitly separates it from get_per_diem_rates and calculate_trip_per_diem, but no sibling is named, so the agent must infer the routing.

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 distinctive 'high-low substantiation method' framing and by the explicit mention of checking a city against the 91 FY2027 high-cost localities. There is no 'use this instead of X when...' statement and no note about when the standard per diem tool would be preferred, leaving the sibling choice to inference.

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