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

Annotations already establish the safe, idempotent, read-only profile, so the bar is lower. The description still adds value beyond them by disclosing freshness ('latest published value'), the batch-snapshot nature ('in a single call'), and the exact SIE series IDs backing each pair. It omits any rate-limit or pagination behavior, which keeps it from a 5.

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 sentences, front-loaded with the core purpose, and every sentence carries information — the series-ID list is bulky but serves as genuine provenance. Slightly verbose in that trailing enumerations could be trimmed without losing meaning.

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?

With an output schema defining return values, annotations covering safety, and a trivially simple optional-parameter surface, the description is nearly complete. It could go further by clarifying the tool's relationship to the single-value banxico.fx.fix_rate sibling, which is the one remaining ambiguity.

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?

There is only one optional parameter ('locale') and schema coverage is 100%, so the schema fully documents it and the description is not required to compensate. Baseline 3 applies; the description adds no parameter-level detail.

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 states a specific verb and resource — 'Get current Banco de México reference exchange rates' — and enumerates exactly which pairs it covers (USD, EUR, CAD, GBP against MXN). An agent can tell this multi-currency snapshot apart from the single-rate banxico.fx.fix_rate sibling without opening the schema.

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?

It offers an implicit use case ('multi-currency MXN conversion and FX monitoring') but never states when to prefer this over banxico.fx.fix_rate or the many other FX-rate siblings. No exclusions or alternative-routing guidance is given, leaving selection to inference.

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