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

With no annotations, the description carries the full burden of behavioral disclosure. It reveals that the tool reads from a free public directory, is non-destructive in nature, and exists to provide polling/dedup/filtering convenience. It does not mention response format, pagination, or rate limits, but for a read-only listing tool the disclosed behavior is reasonably transparent.

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 compact and front-loaded: the core behavior and time window appear in the first sentence, followed by filters and a brief source/value note. No sentences are wasted, and the structure is easy to scan.

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?

Given the moderate complexity (4 optional parameters, no output schema, no annotations), the description covers everything needed to select and invoke the tool correctly: the data source, the time window semantics, all filter behaviors, and the tool's convenience role. The lack of a return-shape description is a minor omission, not a correctness blocker.

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 description coverage is 0%, so the description must compensate fully, and it does. It specifies the valid range for window_hours (1-168, default 24), the allowed protocol values ('x402' or 'l402'), that category is a prefix match, and that payment_network is an exact match with examples. This adds substantial meaning beyond the bare parameter names.

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 opens with a specific verb and resource: 'Return x402/L402 services newly registered on 402index.io within the last window_hours'. It precisely captures the tool's scope (new registrations, time-bounded) and lists optional filters, so an agent knows exactly what this tool does.

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 description gives clear context for when the tool is appropriate: it is a convenience layer over a free public directory, handling polling, dedup, and filtering. It even states what the tool is not for ('not exclusive data access'). However, it names no explicit alternatives or when-not conditions beyond that indirect note.

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