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

Annotations already declare readOnly, idempotent, closed-world, non-destructive, so the safety profile is covered. The description adds genuine behavior beyond that: per-item errors on ambiguous ZIPs, the default fiscal year resolved as 'today in America/New_York', and coverage boundaries (no OCONUS, no FY2028). Rate limits or response shape are not mentioned, but an output schema exists.

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?

Four dense sentences with no filler, front-loaded with the lookup scope before defaults and edge cases. The clause about bundled tables and XLSX/CSV files is slightly compressed, but nothing is expendable.

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 2-parameter read tool with full schema coverage and an output schema, the description covers purpose, default resolution, per-item failure mode, sibling routing, and coverage limits. The only gap is how partial failures surface in the response, which the output schema likely handles.

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%, so the baseline is 3. The description still earns credit for explaining the fiscal_year default semantics (today in America/New_York) and for tying the 25-item cap to the locations array, information the schema states only partially or implicitly.

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 ('looks up monthly GSA CONUS lodging and M&IE rates') with scope (up to 25 ZIPs or City, ST), fiscal years (FY2026/FY2027), and file formats. It also names the sibling calculate_per_diem in its disambiguation role, so an agent can tell the two apart without opening either 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?

Gives an explicit routing rule to the alternative: ambiguous ZIPs yield an item error and 'calculate_per_diem accepts county for disambiguation.' It also states exclusions (OCONUS, FY2028), which is clear context. It does not say more broadly when an agent should prefer calculate_per_diem for other purposes, so it falls short of full when/when-not guidance.

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