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

With annotations already declaring the safety profile, the description adds genuinely non-redundant context: pay-per-call pricing, first 25 free, failed calls free, and the fact that repeats are charged, which explains why idempotentHint=false. 'Reads or computes only and changes nothing' is largely a restatement of readOnlyHint/destructiveHint, but the cost model is real added value.

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?

Core purpose is front-loaded in the first sentence, but the trailing payments sentence drags in '/credits', 'x402 USDC' and card-key detail that is partially redundant with 'each call is charged, so repeats are not free'. Some of the cost clause earns its place; the payment-rail specifics are clutter.

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 two-param converter with no output schema, the description covers inputs and cost but never says what comes back (a string, e.g. 'MMXXVI') nor what happens if both or neither argument is supplied. Adequate but leaves behavioural edges to be discovered.

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% and both parameters are documented, so the baseline is 3. The description goes beyond by stating the 1-3999 range for number and clarifying the mutual-exclusivity mode ('Give either number or roman'), which is not expressed in the schema (required: 0).

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 in both directions ('Convert a number (1-3999) to Roman numerals, or Roman numerals back to a number') and gives the valid range, so an agent knows exactly what it does. It does not differentiate itself from the near-neighbour sibling number_words, so it stops short of a 5.

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 for dates, outlines and puzzles' gives loose context for when the tool applies, and 'Give either number or roman' implies the input-mode choice. There is no explicit when-not guidance and no named alternative among the many siblings.

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