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

Goes well past the annotations (readOnlyHint=false, openWorldHint=true, destructiveHint=false). It discloses the delivery channel and template, that only the subject is per-call configurable, the double-send non-idempotency, the not-found failure mode, the default confirmation prompt and that it can be switched off for this tool, the external-recipient risk, and the required API-key scope. This is unusually rich behavioral context.

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?

Front-loaded with purpose, then progressively narrower operational notes; every sentence carries a distinct fact (template, default subject, copy behavior, error, idempotency, confirmation, auth). It runs long, but no sentence is filler, so it stays efficient despite its length.

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 non-idempotent, externally-reaching mutation with no output schema, the description covers everything an agent needs: recipient scoping, error behavior, duplicate-send risk, confirmation policy, and credential requirements. Nothing material is left 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 description coverage is 100%, so the schema already documents emails, as_copy, subject, invoice_id, and send_copy_to_me. The description restates the subject default ('without one Alegra uses a default subject') and the as_copy original-vs-copy semantics, which adds slight emphasis but no new syntax or constraints. Baseline 3 when the schema does the heavy lifting.

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?

Opens with a specific verb+resource+scope: 'Send a sales invoice by email to one or more addresses.' It also names the underlying mechanism (Alegra's invoice email / 'Correo de envío de facturas de venta' template), so an agent can distinguish it from alegra_create_invoice, alegra_get_invoice, and alegra_list_invoices without 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?

Gives clear conditions: it fails with not-found when the invoice doesn't exist, double invocation sends two emails, and (importantly) 'Reaches other people: confirm with the user before each call.' It doesn't name sibling alternatives, but there is no competing send-email tool among the alegra siblings, so the routing context is effectively complete.

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