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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds value by disclosing that lodging rates vary by month/season and that the tool returns both a monthly lodging ceiling and a flat M&IE rate. However, it doesn't explain behavior around missing cities, invalid state codes, or the exact response shape — with no output schema, a bit more behavioral detail would be useful.

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?

Two sentences plus an example. Every sentence earns its place: the first defines scope and output, the second gives a concrete usage example. No filler or redundant restatement of the name.

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 simple read-only lookup with 100% schema coverage and full annotations, the description covers the core semantics, output values, and an example. The only gap is the lack of an output schema means agents don't know the exact field names in the response (e.g., whether lodging ceiling is labeled 'lodging_rate' or 'monthly_ceiling'), but the description clearly describes the two values 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 description coverage is 100%, so the schema already documents all four parameters thoroughly. The description adds contextual meaning for city and state by tying them to the lookup, and mentions the year default implicitly through the example ('year: 2026'). However, it doesn't add meaning beyond what the schema already provides for _apiKey or year, so baseline 3 is appropriate.

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: 'Get US federal per diem rates' for a city by name and state. It also distinguishes from rates_by_zip by specifying city/state lookup and describes the return values (monthly lodging ceiling and M&IE daily rate). The example call reinforces the purpose.

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 description clearly says when to use the tool: to get per diem rates for a named city and state. It implies the alternative is rates_by_zip (sibling tool) for ZIP-based lookups, though it doesn't explicitly say 'use rates_by_zip for ZIP codes.' The example provides a concrete invocation pattern, which helps the agent understand usage context.

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