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

The readOnlyHint annotation already establishes this as a safe read operation, and the description adds useful behavioral context: it returns the date and value as published and charges $0.003 USDC per call via x402. It does not mention rate limits or authentication requirements, but the core behavior is well disclosed.

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 description is compact and front-loaded: purpose and supported series come first, followed by return behavior and pricing. Every sentence adds useful information without repetition or 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 one-parameter, read-only lookup tool with full schema coverage and a readOnlyHint, the description is complete enough. It states what is returned, what series are accepted, and the per-call cost, so an agent can call it correctly without additional context.

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 the parameter is already documented; the description adds meaning by clarifying that 'fix' is the USD/MXN FIX rate and that raw SIE series IDs are also accepted. It still does not explain the expected format for a raw SIE ID.

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 states it returns the latest value of a Banco de México series and lists concrete aliases like fix, udis, tiie28, and tasa-objetivo. It is specific about the resource and return shape, though it does not explicitly contrast itself with sibling financial 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?

Usage is implied by 'latest value' and the supported series names, but there is no explicit guidance on when to choose this tool versus alternatives. It also does not explain when to use a raw SIE series ID instead of the named aliases.

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