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

With annotations declaring readOnlyHint=false and idempotentHint=false, the description adds genuinely useful context the annotations cannot carry: the $0.005 USDC-on-Solana x402 cost, the exact retry flow with the PaymentRequired challenge, and the _meta["x402/payment"] key. It does not contradict the annotations. It stops short of describing what the response contains or behavior when no watches exist.

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 sentences, front-loaded with what the tool returns, then the payment and transport details an agent needs to actually invoke it. No filler; every clause carries operational 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, no-output-schema tool, the description covers the payment/auth path and the timestamp format well. The main remaining gap is the shape of the returned change records, which no structured field covers since there is no output schema.

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 single 'since' parameter is a bare string in the schema, so the description must compensate — and it does by specifying the format as an ISO8601 timestamp. It stops short of stating inclusivity (strictly after vs. at) or timezone handling.

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 resource and operation: changes to match-state for watched products since a timestamp. An agent can tell this is a change-feed reader distinct from recalls_watch (which registers the watch) and recalls_search (which searches recalls). The jargon 'match-state' is slightly opaque but the intent is recoverable.

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 phrase 'watched products' implies a prerequisite (a watch must already exist via recalls_watch), but this is left implicit rather than stated. No explicit when-to-use/when-not guidance or named alternative appears, only the payment mechanics for actually paying.

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