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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds valuable operational context beyond those annotations: the call costs $0.01 USDC per successful call and the data is specifically pre-ranking movers. This is useful but does not fully describe response behavior.

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 short sentences carry distinct information: what the tool surfaces and its per-call price. There is no filler, and the core concept is front-loaded.

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-required-input, heavily annotated read tool, the description conveys the core data type, its timing advantage, and the pricing constraint. It does not describe the output shape, but with no output schema and low complexity this is a minor gap.

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?

The single `limit` parameter is already fully documented in the schema with min, max, default, and a description. The tool description adds no additional parameter meaning, so baseline 3 is appropriate.

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 names a specific subject: sudden inflow spikes and first-seen large payers, and frames the tool as an early pre-ranking signal. It also differentiates from the general ranking-type siblings. However, it is a noun phrase rather than an explicit verb+resource statement like 'Returns...' or 'Lists...', so it stops short of a 5.

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 'before they show up in a ranking' implies this is for early detection of movers, but the description does not explicitly state when to use this tool over x402_new_entrants or x402_trending_services. Sibling differentiation is left mostly to inference.

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