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

With no annotations supplied, the description carries the full behavioral burden. It discloses a payment/trial constraint (5 free calls per signed wallet), which is genuinely useful, but says nothing about the return shape, rounding/precision behavior, overflow handling, or what happens if several duration parameters are supplied at once.

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?

Two short sentences, front-loaded, with no filler. The leading "Duration Human:" label only restates the tool name and could be dropped, but overall the text is efficient rather than padded.

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 tool with three undocumented, untyped-semantics parameters, no annotations, and no output schema, the description is far too thin. It should at minimum clarify which parameter to use and what the formatted output looks like, since nothing else in the definition supplies that information.

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% across three parameters (ms, value, milliseconds), all typed as plain strings. The description does not map any parameter to meaning, state expected units, or clarify whether these are aliases or alternatives. An agent cannot tell from the definition which input to send.

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?

"Format a duration in human terms" does name a verb (format) and a resource (duration), so the general intent is inferable. However, "human terms" is left vague (no example output format, no unit conventions), and the description does nothing to separate it from close siblings like x402-duration-humanize, x402-duration, x402-duration-iso, or x402-seconds-to-human.

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 when-to-use guidance, no prerequisite, and no mention of alternatives, even though the sibling list contains multiple near-identical duration-formatting tools. The only guidance given is commercial (5 free trial calls), which does not help an agent choose this tool over a sibling.

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