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

Annotations already declare readOnlyHint, idempotentHint and openWorldHint, so the safety profile is covered. The description adds genuinely useful context beyond that: the comparators are assumptions rather than measurements of any bank/provider, and no protocol fee is deducted on this rail — important for interpreting the output.

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, purpose front-loaded, with the caveat about assumptions following immediately. Tight overall, though the named-but-absent parameters cost some clarity.

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?

An output schema exists so return values need not be described, and the assumption/no-protocol-fee caveat is valuable. However, with zero required parameters and no usage guidance against siblings, an agent still lacks routing information to invoke this correctly.

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 description coverage is 100% so the baseline would be 3, but the description names bank_fee_pct and custodial_fee_pct as caller-supplied parameters while the schema contains only amount/amount_usd/amount_usdc/currency. These phantom parameters are misleading and add no reliable value over the schema.

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 operation (arithmetic comparison of a USDC settlement against comparator percentages) and resource (FX savings across fiat currencies), which is enough to distinguish it from siblings like fx_spot_price_oracle or check_price. Not quite a crisp 'verb+resource' formulation, but clear.

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?

No statement of when to use this tool versus alternatives such as fx_spot_price_oracle or check_price, and no prerequisites or exclusions. The only usage-adjacent text is that the comparators are supplied by the caller.

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