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

The description adds meaningful behavioral details beyond the annotations: it specifies the maximum supported value (999,999,999,999), decimal precision (two places), and the 'only' suffix in currency mode. Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description's additional range and format constraints provide good transparency without contradicting them.

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 description is three short sentences with the core action front-loaded, followed by the currency caveat and range limit. It is efficient and free of fluff, though the source URL is extra context that, while useful, is not strictly necessary for invocation.

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?

Combined with the input schema, which documents the value format and commas, and the presence of an output schema, the description gives enough information for an agent to call the tool correctly. It covers the key constraints (range, decimals, currency behavior), though it does not describe error cases for out-of-range or invalid inputs.

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 the baseline is 3, but the description adds value beyond the schema by clarifying that currency mode produces cheque-style output ending with 'only' and stating the range and decimal precision for the value parameter. This enriches meaning beyond the bare boolean description.

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 explicitly states the tool converts a number into written English words, a specific verb+resource combination. It further distinguishes itself with the currency option producing UK pounds and pence in cheque style, which separates it clearly from the many sibling converter tools.

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?

The description gives clear context on when to enable currency mode ('Set currency to true to write it as UK pounds and pence'), which is actionable guidance. It does not mention alternatives or exclusions, but no direct sibling alternative occupies this exact niche, so the context provided is sufficient.

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