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). The description adds genuine behavioral context: newest-first ordering, returned fields, the meaning of a null state, and the important note that it operates on demo/sample data. Pagination behavior is left unstated, keeping 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?

Front-loaded with the core purpose, followed by scoping detail and a short operating note. The 'state of null' sentence drifts toward return-value detail that an output schema would normally carry, slightly diluting tightness but not fatally.

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 read-only list tool with full annotation coverage and an output schema, the description supplies enough purpose and behavioral context to call it correctly. The remaining gap is per-parameter filtering semantics for the ~45% of params undocumented in the schema.

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 55%, so several parameters (number, series, client_cif, canceled, collected, issued_after/before) rely on the schema alone. The description adds useful meaning for doc_type (proformas) and the state values, but does not fully compensate for the uncovered half of the parameters.

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 (List) and resource (invoices) plus scope details: source is the invoicing account, ordering is newest first, and proformas are returned when doc_type is set. This cleanly distinguishes it from invoices_get (single), invoices_issue, and invoices_cancel.

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 'list' and the doc_type hint for proformas, but there is no explicit when-to-use, when-not, or routing to alternatives such as invoices_get. No prerequisites or exclusions are stated, leaving the agent to infer that this is the bulk-retrieval tool.

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