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

Beyond the annotations (readOnlyHint=false, destructiveHint=false), the description discloses that the tool is a paid DATO service that consumes balance, and it points to 'consultar_precios' for the fee. It also states the return content (date and official series), which adds value beyond the annotations. No contradiction exists.

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 compact Spanish sentences front-load the core purpose, then add the cost warning and return description. No filler or redundancy, each clause carries distinct information.

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 2-parameter lookup with an output schema, the description covers the main usage points: optional date, optional amount conversion, cost implication, fee lookup route, and output summary. It falls short only on date format and conversion semantics, which prevents a 5.

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?

With 0% schema description coverage, the description must compensate for the bare schema titles 'Fecha' and 'Monto'. It says both are optional and that 'monto' is for conversion, but it does not specify the expected date format or the direction/currency of the amount conversion (USD to MXN vs MXN to USD), leaving ambiguity.

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 clearly identifies the tool as the official Banxico FIX USD/MXN exchange rate service, with optional date filtering and amount conversion. It states the resource (official Banxico FIX rate), the scope (by date, optional amount conversion), and the observable output (date and official series). Although no sibling is named, no sibling tool provides exchange rates, so it is effectively distinguishable.

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?

The description explicitly warns that the tool consumes balance ('Consume saldo') and directs the user to 'consultar_precios' for the current fee, which is actionable usage guidance. It does not explicitly state when not to use it, but the fee pointer and optional-parameter explanation provide clear context for deciding to invoke it.

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