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

readOnlyHint=true already covers the safety profile, so the description's remaining job is to disclose behavior beyond annotations — it does so with the top-5 cap and the product-name merging rule ('MANGO' + 'MANGO FRESH' = one), which materially changes results and is easy to misread. It stops short of stating default time window behavior, but the merging quirk is the higher-value disclosure.

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, zero filler, with the core behavior and the ranking rule front-loaded and the disambiguation clause second. Every clause earns its place.

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?

With no output schema, the description carries the burden of describing the return, and it does: five products ranked by total cost with merged names. The only gap is the unspecified default date range for an all-optional param set, which an agent choosing to call it would benefit from knowing.

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 both parameters are documented there, so the baseline is 3. The description mentions no date semantics at all and never says what happens when startDate/endDate are omitted (all-time?), which is the one parameter behavior an agent might need to reason about.

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 (Get), resource (top products/items), ranking basis (total cost), result count (top 5), and a non-obvious normalization rule with an example. An agent can distinguish it immediately from get_top_merchants, get_spending_summary, or search_expenses.

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?

Explicitly names the alternative it should displace ('not search_expenses') and enumerates the triggering intents ('what they buy most', 'suggesting a recipe from frequently-bought ingredients'). This is exactly the when-to-use/when-to-use-something-else guidance the dimension asks for.

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