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

With no annotations, the description carries the full burden and mostly fails. It discloses a payment/trial model ('5 free trial calls per signed wallet'), implying wallet signing is required, which is genuinely useful. But it says nothing about window semantics, minimum data requirements, edge behavior, or output shape.

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?

One tight front-loaded sentence stating the operation, plus a short trial-call note. No padding, though the emoji pricing banner is slightly noisy relative to the technical substance.

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?

A two-param math tool with 0% schema coverage, no annotations, and no output schema. The description should at least define input formats and window behavior; instead it omits both, leaving the agent guessing how to construct a valid call.

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%, so the description must compensate. It references both parameters by name with meaning ('values array', 'window'), which is more than the bare schema gives, but adds no format or type detail (is values JSON, comma-separated, how is window counted).

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: 'Computes the rolling population standard deviation across a window of the values array.' This distinguishes it from a plain moving-average or non-rolling population stddev. It does not, however, explicitly name or route away from siblings like x402-moving-average, x402-population-stddev, or x402-pooled-std.

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?

No when-to-use guidance, no prerequisites, no named alternatives. The agent is left to infer that this is for time-series windowed dispersion rather than the many other stddev/rolling siblings.

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