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

The description adds meaningful behavior beyond annotations: zero state mutation, public unauthenticated access, and a rate limit of 60 requests/min per IP. These are operationally relevant details for invoking the tool correctly and do not contradict the read-only, idempotent annotations.

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?

The definition is front-loaded with the core purpose and organized into useful usage, behavior, and return sections. It loses some efficiency because the when-to-use sentence is tautological and the parameter line duplicates the schema.

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 annotation coverage, the description supplies the remaining context an agent needs: scope, alternatives, auth/rate-limit behavior, and a return-shape summary despite there being no output schema.

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?

The single parameter has 100% schema description coverage with examples, so the schema already carries the semantic burden. The description only repeats that address_or_suburb is required and adds no format or interpretation guidance beyond the schema.

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 first sentence states a specific verb and resource: checking delivery eligibility for an address or suburb and calculating estimated fees, scoped to Pretoria/Gauteng purified water delivery. This is clear enough for an agent to distinguish it from product, cart, and order-status siblings.

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?

It explicitly names alternatives such as list_products, create_checkout_cart, and track_order_status and says not to use this tool when another specialized tool fits. However, the positive when-to-use guidance is circular ('when you specifically need to execute check_delivery_coverage') rather than stating a concrete selection condition.

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