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

The annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds real context beyond that: the deadline target is fixed at December 25, the scope is exactly one ZIP, and the valid prefix ranges are enumerated. It does not say what happens for an out-of-range ZIP, which keeps it from a 5.

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?

One dense sentence, front-loaded with the outcome (send-by dates for December 25), followed by the input restriction and covered mail classes. Every clause carries information; there is no filler.

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 single-parameter read-only lookup with no output schema, the description is nearly complete: it establishes the deadline, the input domain, and the mail classes returned. The only gap is that it does not characterize the response (e.g., a date per mail class), which would help an agent know what to expect.

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% and the single parameter is documented, so the baseline would be 3. The description earns an extra point by constraining the value semantically, tying the ZIP to APO/FPO/DPO prefixes (090-099 AE, 340 AA, 962-966 AP) rather than the schema's bare examples.

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 names the exact resource (USPS holiday send-by dates for December 25 delivery), the constrained input domain (one APO/FPO/DPO ZIP code with prefixes 090-099 AE, 340 AA, 962-966 AP), and the four mail classes covered. That APO/FPO/DPO scoping implicitly separates it from the general-purpose siblings check_holiday_ship_by_date and get_usps_holiday_shipping_deadlines.

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 scope: a military-mail ZIP in the listed ranges means use this tool. However, there is no explicit when-to-use/when-not statement and no sibling tool is named as the alternative for domestic or non-APO ZIPs, leaving the routing decision to inference.

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