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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description earns credit by disclosing the fallback behavior when interest_rate is omitted — the default is the Banco de México average of advertised fixed-rate offers for the latest month — and by naming the additional reported figures (average CAT, Banxico target rate). It stops short of describing calculation assumptions or rounding.

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?

A single dense sentence with the country marker and primary outputs front-loaded, and no filler. It is packed but every clause (default rate source, extra outputs) carries 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?

There is no output schema, so the description must carry the return values, and it does name monthly payment, total interest, average CAT, and the Banxico target rate. Combined with full parameter coverage, this is nearly complete; only calculation conventions remain unstated.

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 baseline is 3, but the description adds real meaning beyond the schema: it explains what the optional interest_rate parameter defaults to and what source that default comes from, which the schema's '% a year (optional)' does not convey.

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 names a specific output (monthly payment and total interest) for a specific resource (fixed-rate peso mortgage) and pins the scope with 'MEXICO.' and 'peso'. This clearly separates it from mortgage_payment_br and mortgage_payment_es without the agent opening any 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?

Usage is implied by the country and currency markers, so an agent can infer this is the Mexican mortgage calculator, but there is no explicit when-to-use statement, no exclusion, and no pointer to alternative siblings. Adequate but with a clear gap.

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