beel_get_recurring_next_occurrence

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

Annotations already declare readOnlyHint=true, openWorldHint=true, idempotentHint=true, and destructiveHint=false, meaning the agent knows this is a safe, idempotent, read-only operation. The description adds the key behavioral fact that 'Nothing is persisted and no numbering is consumed,' which is a critical side-effect explanation beyond the annotations. It also warns about fiscal guardrails and refers to resources that affect outcome, adding context. There is no contradiction with annotations.

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 moderately sized and reasonably front-loaded with the main purpose. The first sentence clearly explains the function and non-persistence. The safety warnings are useful but are placed in a block with emoji and indentation, which is somewhat verbose and might be trimmed. Overall, each section contributes value, but it's not as tight as it could be—the endpoint line is redundant with the description and schema.

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?

Given the tool has 2 parameters, no output schema, and high-level annotations covering safety, the description covers the critical non-persistence behavior and references external guardrails. However, it doesn't describe the return value format or any potential errors beyond what the schema mentions for company_id. The reference to 'fiscal guardrails' is helpful but the description could be more complete by explicitly stating what the response contains (e.g., the invoice object with computed amounts/taxes). Still, it is reasonably complete for a read-only preview tool.

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 only 50%: company_id has a detailed description (UUID, NIF, context derivation, 403 errors, non-disclosure), but recurring_invoice_id has no description. The description does not explain the format or semantics of recurring_invoice_id beyond the schema's UUID format. Since coverage is partial, the description could compensate by explaining what recurring_invoice_id refers to (the recurring template ID), but it does not. However, company_id's rich schema description carries most of the semantic weight, so the score stays above baseline but below perfect.

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 the tool returns the invoice that would be produced by the next generation of a recurring template, and explicitly notes nothing is persisted and no numbering is consumed. It differentiates from siblings like beel_generate_recurring_invoice_now (which likely generates/creates) by emphasizing the non-mutating preview nature. While it names the endpoint and operation, it doesn't explicitly contrast with all get_* siblings, but the core purpose is unambiguous.

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?

The description includes a caution to read fiscal guardrails before calling and points to two specific resources (beel://guardrails/invoice-types and beel://guardrails/regime-keys) along with a recommendation to call beel_docs_search for exhaustive rules. It implies this is a read-only preview and that it should be used when the caller wants to see the next occurrence without persisting. It does not explicitly list when not to use this tool versus alternatives, but the safety guidance and reference to docs provide a clear context for correct usage.

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