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

Annotations already declare readOnlyHint=false, idempotentHint=true, destructiveHint=false, so the safety profile is covered. The description adds genuinely new context: the required OAuth scope (favorites:write), the note that order/buyer state changes, and the public-product restriction. It does not explicitly restate idempotency, but that is already in 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?

Two dense sentences with zero filler, front-loaded on what the tool does, followed by alternatives and auth requirements. Every clause carries routing or prerequisite information.

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 mutation with an output schema, the description covers purpose, alternatives, auth scope, and state effects, and hints at the public-product constraint. Return values need no explanation given the output schema; only minor gaps remain (e.g., what happens on an already-favorited product).

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 the single product_id parameter is documented in the schema with a clear disambiguation (internal product ID, not SKU/article or basket item ID). The description adds nothing parameter-level, so the baseline of 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?

States a specific verb and resource ('Save a current public product in this buyer's favorites') and immediately contrasts it with the basket, which is the most likely confusion given the sibling add_cart_item. An agent can distinguish it from get_favorites/remove_favorite/add_cart_item without opening any 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?

Names three concrete alternatives and the condition that selects each: get_favorites to inspect the list, remove_favorite to undo, add_cart_item for a purchase basket. The 'without adding it to the basket' clause explicitly rules out the wrong sibling for this intent.

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