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

Annotations already declare readOnly/idempotent/non-destructive and openWorld=false, so the safety profile is covered. The description adds value the annotations cannot: it states the data vintage (2023 USDA zone) and that a citable source link is returned, which matters for an agent that must attribute output.

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: trigger first, return payload second. Zero filler and the most decision-relevant information is front-loaded.

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 lookup with full schema coverage and annotations, nothing an agent needs is missing. Because there is no output schema, the description correctly compensates by enumerating what comes back (zone, temperature range, source link).

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% — the single `zip` parameter is documented with a pattern and an example. The description confirms the U.S. ZIP context but adds no format or edge-case detail beyond the schema, so baseline 3 applies.

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?

Names a specific verb+resource (USDA plant hardiness zone for a U.S. ZIP) and even gives the output shape (e.g. 7a). The scope is unmistakably distinct from the frost-date, planting-calendar and what-to-plant siblings without needing to name them.

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?

Opens with an explicit trigger: 'Use this when the user asks what USDA plant hardiness zone ... a U.S. ZIP code is in, or the average extreme winter low there.' It gives clear positive context but names no exclusions or alternatives among the sibling tools.

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