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

Annotations already declare idempotentHint=true, destructiveHint=true and openWorldHint=true; the description adds the genuinely new fact that the call consumes a plan quota ('counts against the plan limit'), which a caller must know before invoking. The 'already tracked changes nothing' sentence restates the idempotency annotation rather than extending it, and auth/plan-limit-exceeded behavior is not described.

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 short sentences, front-loaded with the action and input forms, followed by the no-op and quota facts. Every sentence contributes a distinct constraint and nothing is repeated.

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 two-parameter write tool with no output schema, the definition covers inputs, exclusivity, idempotency and quota cost. The main omission is what the call returns (a tracked-product record or identifier) or what the error looks like when the plan limit is reached, which would help an agent interpret the result.

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 0% and the schema marks neither parameter as required, so the description carries the burden by imposing the mutual-exclusivity rule ('exactly one of the two'), which the schema cannot express. It also expands 'gtin' into EAN/UPC, adding meaning absent from the bare string type; only the 8-14 length constraint is left to the schema.

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 ('Adds a product to the tracked list') and immediately names the two accepted input modes (marketplace URL or GTIN). The verb 'adds' cleanly separates it from read-oriented siblings like list_tracked_products and get_product_offers, so an agent can pick it 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?

Gives clear preconditions: 'exactly one of the two' input forms, and notes that re-adding an already tracked product changes nothing, which tells the agent it need not pre-check for duplicates. It stops short of explicitly naming an alternative (e.g. use list_tracked_products to verify what is already tracked), so it lacks full when-not guidance.

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