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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive behavior. The description adds that the data is from an official government source and a free API, which informs reliability and access expectations, but does not detail rate limits or authentication (though 'free API' implies no auth).

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?

Four compact sentences, front-loaded with the core purpose. Each sentence contributes: purpose, context, return format, and source. No 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 simple two-parameter read-only FX rate tool with a complete schema and output schema, the description provides all necessary context: what it returns, the date format, and source reliability. Nothing an agent needs 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 description coverage is 100%; both parameters are fully documented in the schema with patterns and descriptions. The description reinforces the date-range concept and format but adds no new syntax or constraints beyond 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 verb 'Get' and the exact resource 'Banco de México FIX USD/MXN exchange rate', including the series identifier SF43718. This clearly distinguishes it from the sibling banxico.fx.rates and other FX 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?

Provides context that the FIX rate is used for settling foreign-currency obligations, implying when it is relevant, but does not explicitly state when to use this tool versus banxico.fx.rates or other exchange-rate tools. No exclusions or alternatives are named.

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