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

Beyond the annotations (readOnly, idempotent, openWorld), the description discloses the return fields (devanagari, grouped, units{crore, lakh,...}, wordsEnglish, wordsNepali, currency{formatted, wordsEnglish, wordsNepali}) and the cost model: $0.001 per call from Exepal credit, no charge on failure, plus free daily calls. Pricing and failure-billing behavior are exactly the kind of operational context annotations cannot supply.

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 conversion scope and the usage cue come first, followed by return shape and then pricing, which is a sensible front-loading order. The long 'Use to write...' sentence is comma-heavy and slightly run-on, but no sentence is filler.

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-parameter, idempotent formatting tool with an output schema, the description covers trigger, both input modes, output fields, currency behavior, and billing. Nothing an agent needs to call it correctly or predict cost 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 both parameters are already documented, and the description largely restates them (accepted Devanagari digits/commas/currency signs; currency adds rupee/paisa wording). It adds a little framing by tying currency to invoice/cheque use, but no format or edge-case detail beyond the schema, so the baseline 3 applies.

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 opens with a specific verb+resource: converting a number to Devanagari digits, lakh/crore grouping, and English (Indian system)/Nepali words, plus NPR/INR amount wording. That scope is unmistakably distinct from the sibling tools (south_asia_date, south_asia_forex, south_asia_id, south_asia_phone), so an agent can select it without opening the schema.

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?

It gives concrete when-to-use guidance: 'Use to write an amount the South Asian way... for invoices and cheques,' with enumerated output modes (grouping, words, Nepali words, Devanagari digits, rupee/paisa wording). It does not state exclusions or point at an alternative tool, but the domain is narrow enough that the intended trigger is clear.

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