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

With readOnlyHint=true already covering the safety profile, the description adds real value by declaring precedence: 'A customer's own saved values override these on their invoices.' That prevents misreading the result as the effective values for a specific customer. It does not mention tenant/auth scoping beyond 'tenant', but that is minor.

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 sentences, front-loaded with the returned content. The parenthetical Spanish synonyms (plazo de pago / días de vencimiento, tipo de IVA por defecto) add domain vocabulary useful for Spanish-invoicing users but slightly clutter the sentence.

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 carries the burden of describing return values, and it names three concrete fields plus the override rule. It may still be missing other defaults the endpoint returns (e.g. series or footer defaults), which keeps it short of 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?

The tool takes zero parameters, so the baseline is 4. The description correctly implies a single-tenant read with no filtering options, matching the empty 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 and resource ('Get the tenant defaults a new invoice starts with') and enumerates the exact contents: payment term in days, IVA rate, and retención visibility. This scope ('tenant defaults for a new invoice') cleanly separates it from get_invoice, get_invoice_display and get_invoice_footer.

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 only implied: an agent can infer it should call this before create_invoice to learn tenant defaults. There is no explicit 'use set_invoice_defaults to change these' pointer and no statement of when this is unnecessary, so the routing guidance is left to inference.

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