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

Annotations already cover the safety profile (readOnlyHint, idempotentHint, destructiveHint=false), yet the description adds substantive behavior beyond them: results are sorted biggest-saving-first, restricted to in-stock items, non-public codes are never surfaced, and checkout applies the final price. These constraints materially affect how an agent should interpret and present the 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?

Three sentences, front-loaded with the selection criterion, then output contents and caveats, then next actions. Every clause carries distinct information (trigger, contents, sorting, exclusions, pricing authority, routing) with no filler.

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 read-only, single-optional-param tool with an output schema that already defines the return shape, the description covers trigger, contents, ordering, caveats, and next steps. Nothing an agent needs to select or 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?

Schema description coverage is 100% and there is a single optional 'limit' parameter fully documented with range and default, so the schema carries the weight. The description adds ordering/stock behavior but nothing about the limit argument itself, making 3 the appropriate 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 (lists products on sale) plus the three things it returns: discounted products with usual price and end date, public offer codes, and the free UK delivery threshold. This is clearly distinguishable from siblings like find_products or get_product, which cover non-sale catalog data.

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 person asks about offers, discounts, codes or what is on sale at teas.co.uk') and closes with concrete routing to the next tools (get_product, quote_cart, add_to_basket) mapped to the follow-up intent. Both when-to-use and what-to-do-next are stated, not inferred.

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