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

Annotations already declare a safe, idempotent, read-only, open-world call, so the bar is lower. The description still earns credit by disclosing business rules not in structured fields: the 1:00 PM local-time same-day cutoff, Monday–Saturday operation, and that failures return a reason when known.

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 sentences, front-loaded with the core question the tool answers, then scope, then timing rules, then failure behavior. Slight redundancy in restating the same-day cutoff and reason cases separately, but nothing is wasted.

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?

An output schema exists so return values needn't be spelled out, yet the description still tells the agent the result carries a reason field. For a two-param read-only availability check, the timing rules and failure semantics close every gap an agent would encounter.

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 both zip (5-digit US ZIP) and date (YYYY-MM-DD, recipient local date) are already fully documented. The description adds only the framing that availability is per ZIP and date and the local-time-zone cutoff, which is a modest gain over the schema baseline.

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 (check delivery availability), and pins the scope precisely: per US ZIP code and one specific date, explicitly 'not per arrangement.' That scope statement also separates it from arrangement-level siblings like get_arrangement_details and search_arrangements.

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?

Implicit usage is clear from 'one specific date,' and the Sunday/past-date notes hint at when a check will fail. However, it never names an alternative such as next_available_delivery for finding a workable date, so the agent must infer the routing from sibling names alone.

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