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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so safety needs no explanation. With no output schema, the description carries the return-value burden and does it well by showing the exact rendered string, including the "Rupees and ... Paise Only" phrasing and paise handling. It doesn't say what happens for values over the ceiling or with more than two decimals.

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?

Two sentences, front-loaded with the purpose, and the second sentence is a worked example that does real spec work rather than padding. Nothing extraneous.

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 one-parameter formatter with no output schema, the description plus schema covers what an agent needs: purpose, convention, range, and the exact output shape. Only edge cases (zero, negative, over-limit amounts) are unaddressed.

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?

The single parameter has 100% schema description coverage including the ₹99,99,99,999.99 ceiling, so the baseline is 3. The example input (125050.50) confirms the accepted numeric form, but the description adds no guidance on the string variant the schema also allows.

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+resource (write a rupee amount in words) and pins down the numbering convention (lakh/crore, Indian way). The worked example makes it unmistakable and clearly separates it from the sibling calculators, which compute rather than format.

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?

"as on invoices, receipts and cheques" gives a clear context in which this formatting is the right choice, which is enough to route an agent here instead of to calculate_gst or calculate_upi_mdr. It stops short of naming exclusions or an alternative formatter, so it isn't a full when/when-not statement.

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