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

No annotations exist, so the description carries the full behavioral burden. It discloses the return type and a quota ('5 free trial calls per signed wallet'), implying billing/auth. However, it omits default date behavior, timezone handling, and whether it is a pure read operation.

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?

Short and front-loaded, with the core behavior first and the quota note second. The leading 'Prev Month:' is slightly redundant with the name, but overall there is little waste.

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 simple date calculation with no output schema, the description states the return format and input relation. Yet it is incomplete on default behavior, timezone details, and parameter format, leaving an agent with avoidable ambiguity.

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% for the single 'date' parameter. The description says 'given date' but never explains format, optionality (it is not required), or what happens if the parameter is omitted. It fails to compensate for the schema gap.

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?

Specific verb 'Returns' and resource 'ISO timestamp of the first day of the month before the given date'. Clearly describes the calculation, but does not explicitly distinguish itself from date siblings like x402-next-month or x402-month-start.

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?

Provides no when-to-use guidance, no alternatives, and no exclusions. The description only states the return value and trial quota; an agent must infer when this tool is appropriate.

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