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

Beyond the annotations, the description discloses genuinely useful behavior: accepted range (up to trillions, negatives), that decimals trigger a cheque-form output with 'and' cents, and a per-call cost of $0.001 USDC via x402. The payment/cost detail is significant and not derivable from annotations, though rate limits and error behavior are unstated.

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?

Three tight sentences, front-loaded with the core purpose and followed by scope, usage cue, and the critical cost note. Every sentence carries information an agent needs and nothing is padding.

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, no-output-schema utility, the description covers purpose, input range, decimal handling, output shape, and cost. Nothing essential for correct invocation is missing.

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 100%, so baseline is 3, but the description adds real constraints the schema omits: the range ceiling (trillions) and that negatives are permitted. The single 'number' parameter is thus better understood than from the schema alone.

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 specific verb+resource: converting a whole number into English words, with concrete use cases (cheques, invoices). It is easy to distinguish from the nearest sibling number_roman, but it never names or contrasts with that sibling explicitly.

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?

"Use when amounts must be written out in full" states the triggering condition clearly, and the cheque/invoice examples reinforce it. There is no explicit when-not or named alternative, so it stops short of a 5.

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