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

With annotations only covering the generic mutation profile (readOnlyHint=false, openWorldHint=true, non-idempotent, non-destructive), the description carries the rest and does so richly: daily re-checks, emailed digests, the exact change triggers for Amazon and Shopify, a 2-credit recurring charge billed now and every 7 days, a 25-watch cap, and that it only affects the caller's own list. The recurring billing detail in particular is behavior an agent cannot infer from the schema or 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?

The description is long but front-loaded with the two invocation modes, then organized into Amazon triggers, Shopify triggers, and cost/limits. Nearly every clause carries distinct information, though the trigger lists could be tightened slightly.

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 no-output-schema mutation tool with zero required parameters, the description supplies everything needed: what each parameter selects, what will be monitored, how often the user is notified, the recurring cost, and the watch cap. Nothing material is left for the agent to guess.

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%, so the baseline is 3, but the description adds real semantic value by framing asin and store_url as mutually exclusive alternatives — important given the schema marks zero parameters as required. It does not discuss the marketplace parameter, though the schema documents it fully.

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 gives a precise verb+resource ('Start watching an Amazon product ... or a Shopify store') and immediately distinguishes the two modes by their required argument (asin vs store_url). It is also clearly separable from the sibling tools watch_list and watch_remove, which manage rather than create watches.

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 states the condition that selects each mode ('pass asin' vs 'pass store_url') and surfaces real constraints: max 25 watches and 2 credits per item per week. It never names watch_list or watch_remove as the alternatives for viewing/removing, so routing guidance is good but not fully explicit.

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