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

With no annotations, the description carries the full load: it does disclose the output shape (suffix + two decimals) and that it is a trivial deterministic transform, which is genuinely useful. It is silent on edge behavior that matters for a formatter - negative numbers, values below 1000, non-numeric input, and very large magnitudes beyond T - and does not state the payment/trial mechanics beyond the free-call line.

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 tight sentence with the example front-loaded where it does the most work, followed by the trial-call note. No redundant restating of the tool name beyond the leading label.

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 single-parameter pure formatter with no output schema, the description gives enough to call it correctly and predict the return string's shape. The remaining gap is input-validation behavior for malformed or out-of-range values.

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 parameter is typed as a string with no documentation, leaving ambiguity about whether digits, commas, or decimals are accepted. The description compensates only partially: the example shows a plain integer input, but does not say the value must be passed as a string or how separators are handled.

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?

Names a specific transformation (compact human number with K/M/B/T suffixes and two decimals) and backs it with a concrete example, 1250000 -> 1.25M, which is unmistakable. It does not name or contrast with nearby siblings such as x402-format-thousands, x402-number-humanize, or x402-format-fixed, so an agent must infer the difference from the spec alone.

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?

Usage is only implied by the example; there is no statement of when to pick this over the many alternative formatters in the sibling list (thousands separators, scientific notation, data-size humanize). The pricing note is the only extra context given.

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