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

Adds real behavioral context beyond the annotations: a cap of 14 dates, a 1:00 PM local-time same-day cutoff, and a remaining-time-before-cutoff value. The annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so this supplementary timing logic is the value-add — though it doesn't say what happens outside the US or when no dates are available.

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?

A single dense sentence that front-loads the result set size, then the three derived fields. Every clause carries information; nothing is padding.

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 one-parameter read-only tool with full annotations and an output schema, the description covers the search domain, output shape, and the timing rule that governs same-day results. Nothing an agent needs in order to call it correctly is missing.

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?

Only one parameter and schema coverage is 100%, with the schema already documenting the 5-digit US ZIP pattern. The description adds little beyond 'available to a US ZIP code' — it does not say whether the ZIP must be the recipient's or how invalid/unserviceable ZIPs behave. Baseline 3 applies since the schema does the work.

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: lists upcoming delivery dates scoped to a US ZIP code, plus the earliest date and same-day feasibility. An agent knows exactly what it returns, though it never distinguishes itself from the sibling check_delivery, which likely overlaps on deliverability questions.

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 rather than stated: an agent can infer this is for 'when can this be delivered' questions, but there is no explicit when-to-use, when-not-to-use, or pointer to check_delivery as the alternative. Nothing is stated about what to do when the ZIP is not serviceable.

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