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

No annotations are provided, so the description carries the full burden of disclosing behavior. It only states that a duration will be formatted as ISO 8601, but it does not reveal how the three schema parameters interact, what happens with invalid input, or whether the tool converts from another duration format. The ambiguity around the 'iso' and 'input' parameters further obscures actual runtime 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?

The description is a single concise sentence with no filler, which is structurally efficient. However, it is so minimal that it omits crucial parameter disambiguation and input-format context, making it under-specification rather than skillful conciseness.

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 confusing three-parameter schema, the lack of annotations, and the absence of an output schema, this description is insufficient for an agent to reliably select and invoke the tool. A simple tool still needs at least one example of expected input or clarification of the parameter relationship to be contextually complete.

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?

While schema coverage is 100%, each parameter description is purely tautological ('Iso to process', 'Input to process', 'Duration to process') and provides no real semantic value. The tool description does not clarify which parameter is the primary input or whether they are aliases. An agent cannot confidently determine whether to pass 'duration', 'iso', or 'input' based on the available text.

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 states a specific verb ('Format') and resource ('a duration as ISO 8601'), clearly identifying the tool's core capability. It is not a tautology of the name and adds the meaningful detail that the output follows the ISO 8601 standard. It does not explicitly differentiate from sibling tools like x402-duration or x402-duration-human, but the core purpose is unambiguous.

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 guidance on when to use this tool versus siblings such as x402-duration, x402-duration-human, or x402-duration-humanize. The description does not mention what input formats are expected, whether conversions are supported, or any conditions that would make this tool the right choice. An agent must infer usage entirely from the name and abbreviated description.

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