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

With no annotations, the description does add some behavioral facts: the return is a whole number of days and the call is metered ('5 free trial calls per signed wallet'). It omits how 'now' is defined (timezone/clock), whether the result is signed for future dates, and rounding behavior, which matters for a time tool.

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 purpose is front-loaded in a single tight sentence with no filler. The appended free-trial promo is boilerplate noise, but it is brief and does not bury the operative clause.

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 one-parameter tool with no annotations and no output schema, the description adequately conveys the return (whole days) but leaves the input date format, default handling of the optional parameter, and timezone/now semantics undefined. It is minimally usable but not 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?

Schema description coverage is 0% and the single 'date' parameter is optional with no stated format, yet the description only says 'a given date' without specifying ISO-8601, epoch, or another accepted format. It adds no semantic detail beyond the bare parameter name.

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 gives a precise verb and result: 'returns the whole number of days elapsed from a given date to now,' which is unambiguous about direction (past date → present). It doesn't name or contrast with the many similar siblings (x402-days-between, x402-days-until, x402-time-ago, x402-elapsed-time), so an agent must infer the distinction.

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 when-to-use guidance and no alternatives named, despite several overlapping siblings covering elapsed-time and day-count computations. The only conditional content is a pricing note ('5 free trial calls per signed wallet'), which is not selection guidance.

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