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

Annotations already declare read-only, non-destructive, open-world behavior, so the safety profile is covered. The description adds real operational context beyond that: a cost of 2 credits and the fact that paid plans unlock the zone code, Celsius values, and survival recommendations, meaning free-tier output is a subset.

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 tight sentences that front-load what is returned and end with the billing note an agent needs before calling. The only waste is the redundant restatement of the title ("USDA Hardiness Zone: USDA Hardiness Zone looks up...").

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-value explanation is not required, and for a single-parameter lookup the description covers input scope, cost, and tier-gated fields. It omits what happens with an invalid or non-US ZIP, which is the one gap for an open-world lookup.

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 there is a single required parameter, so the schema already carries the syntax. The description still adds the non-obvious constraint that only US ZIP codes are valid input, which is genuine meaning beyond the schema text.

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 the plant hardiness zone by ZIP code") and scopes the input to US ZIP codes, which distinguishes it from broader siblings like Weather or ZipCodesLookup. It never names an alternative sibling, so the differentiation is inferred rather than explicit.

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 only implied by the purpose statement; there is no statement of when to prefer this over ZipCodesLookup, ZIPDemographics, or Weather. The mention of paid-plan extras gives a hint about tier expectations but not about task selection.

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