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

Annotations already declare destructiveHint=false, idempotentHint=true, and openWorldHint=false, so the safety and repeat-call profile is covered. The description adds the notion of 'one canonical product' and metadata provenance from the product card, but says nothing about what happens when the item is already favorited, limits, or auth requirements.

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 tight sentences: the core action first, the parameter-sourcing hint second. Nothing redundant, nothing buried.

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 six-parameter additive tool with annotations covering idempotency and non-destructiveness and no output schema, the description covers the essential call-shaping information. It is only slightly short on error/edge-case behavior and authentication context.

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?

With 0% schema description coverage, the description must carry the load, and it does add meaning: it names four of the six fields and tells the agent where to source their values (the product card), which is the key ambiguity. The remaining gap is that the channel enum values and the meaning of source/sourceSchemaVersion are still unexplained.

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 (add) and resource (one canonical product, optionally with a configuration) to favorites, which cleanly separates it from favorites_list and favorites_remove. It does not explicitly name those siblings, but the operation is unambiguous from the verb.

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?

The second sentence gives a concrete usage instruction: copy collection, channel, source, and sourceSchemaVersion from the product card 'when available'. That is real guidance on how to populate optional fields, but there is no statement of when to prefer this over alternatives, or of prerequisites such as being signed in.

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