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

With no annotations, the description must carry the behavioral burden, and it does disclose one important trait: an unparseable date returns a 400, plus the paid-call model (5 free trial calls per signed wallet). It omits what happens when 'date' is absent (0 required params), what the default format is, and whether output is a string or object.

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 compact sentence front-loads the core behavior and appends the error case and pricing note. Nothing is redundant, though the emoji pricing line sits oddly mid-definition and competes with the functional content.

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 two-parameter, no-annotation, no-output-schema tool, the definition covers output forms and one failure mode but leaves default-parameter behavior and accepted date input syntax unspecified. An agent could call it, but would be guessing about the no-argument case.

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% with two undocumented parameters, so the description must compensate. It partially does by revealing that 'format' accepts the values 'date' and 'time' to select a slice, which is enum-like information absent from the schema. However, the accepted input forms for the 'date' parameter remain unexplained.

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 verb and resource (format a date) and states the output forms: an ISO-8601 string, or the date/time slice when format is 'date' or 'time'. That distinguishes it functionally from pure parsers or converters, though it never names which sibling to prefer (e.g. x402-parse-date, x402-format-time12).

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?

There is no explicit when-to-use or when-not guidance and no named alternative, despite a dense sibling set of date/time tools. The implied usage ('normalize a date to ISO-8601') can be inferred, but routing between this and x402-date, x402-rfc3339, or x402-format-time24 is left entirely to the agent.

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