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

Annotations already cover safety (readOnly, idempotent, non-destructive), and the description adds genuinely new behavioral context: a plan-level availability gate and the fallback behavior ('it explains that the report isn't included') rather than erroring silently. The main remaining gap is whether individual invoices are returned or only aggregates.

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 what the report returns, followed by the gating caveat. The bucket enumeration is informative rather than filler, and every clause carries information an agent needs.

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?

With no output schema, the description steps in to explain the return structure (count and amount per currency) and the plan-gated failure mode. It is nearly complete for a parameterless report; only the granularity of the result (aggregate buckets vs. invoice rows) is left ambiguous.

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?

There are zero parameters, so there is nothing to disambiguate and the baseline applies. The description correctly avoids inventing parameter commentary and instead spends its words on output shape.

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 ('Get') and resource ('unpaid invoices'), plus the exact grouping scheme (current, 1-30, 31-60, 61-90, 90+) and aggregation shape (count and amount per currency). This clearly separates it from siblings like get_revenue_report or get_expense_report without needing their schemas.

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 use case is implied by 'unpaid invoices grouped by how overdue they are,' and the plan prerequisite (Pro and above) is stated. However, there is no explicit when-to-use vs. when-not guidance or pointer to a sibling report for related analysis, so routing still requires inference.

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