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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the description does not need to restate safety. It adds real behavioral context instead: default mode returns aisles with only a few products each, whereas an aisleId returns all of the user's products in that aisle, and results carry ids usable with add_to_cart. It stops short of describing result size, ordering, or pagination behavior.

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, all load-bearing, with the core purpose front-loaded and the mode behavior and downstream caveat following in logical order. Nothing repeats the schema or annotations.

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 single-optional-parameter read tool with no output schema, the description covers purpose, both modes, and result usability well enough to call correctly. The remaining gap is a lack of detail on return shape beyond 'a few products each' and on how large a full aisle listing can be.

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 already documents aisleId's pattern and 'leave out for the overview'. The description still adds meaning by contrasting what the output looks like in each mode and by clarifying that the aisleId value itself originates from a prior get_favorites call, which the schema states only briefly.

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 description uses a specific verb and resource ('List the products the user buys at Picnic, per aisle') and scopes it to purchase history, which separates it from catalog-oriented siblings like search_products and get_product. An agent can identify this as the favorites/usual-groceries tool without opening the schema.

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 names concrete usage scenarios ('what do I usually buy?', 'my usual groceries') and explains both operating modes: the no-argument overview versus passing an aisleId for a full aisle listing. It also gives downstream guidance ('add only the ones the user asks for'), so an agent knows both when to call it and how to act on results.

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