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

Annotations are absent, so the description carries the full behavioral burden. It discloses that the result derives from a millisecond difference, but says nothing about timezone handling, input format expectations, behavior on invalid or reversed dates, or error responses.

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 core sentence is front-loaded and efficient, but the trailing emoji and free-trial promo add non-functional clutter that dilutes an already short definition.

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?

With no annotations, no output schema, and four undocumented parameters including a duplicated pair, the definition leaves too much for the agent to infer about how to call the tool correctly or what it returns.

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% across 4 params, and the schema exposes two apparent pairs (a/b and start/end) with identical string types. The description names only start and end, leaving a and b entirely unexplained and the ambiguity between the pairs unresolved.

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 days, hours, minutes and seconds between start and end dates') and names the returned units, so the operation is unambiguous. It does not differentiate from close siblings like x402-days-between or x402-hours-between, which compute overlapping quantities.

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 guidance on when to use this over the many sibling date-difference tools (days-between, hours-between, date-math, duration). The only extra content is a promotional trial-call note, which does not help tool selection.

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