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

With no annotations, the description carries the burden and does meaningful work: it discloses that only issued invoices count, that payments already recorded are subtracted, and that results are grouped by client and currency. It leaves unstated the read-only nature (only implied by 'List'), result ordering, and whether pagination applies.

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, both earning their place: the first front-loads the operation and its exact computation, the second supplies the use case. No filler or repetition of the tool name.

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 six-parameter read-only aggregation with no output schema, the description conveys what is computed and how it is grouped, which is what an agent needs to call it correctly. Missing are result ordering and the shape of the returned per-client rows, which matter somewhat given no output schema exists.

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 100%, so the baseline is 3, but the description adds the aggregation semantics that the schema cannot express: what counts as 'outstanding' and how grouping works. It still does not connect the date filters to the 'issued on' basis the way the schema does, so the added value is meaningful but partial.

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 ('List outstanding invoice balances per client'), then defines the metric precisely as sum of totalDue minus recorded payments for issued invoices, grouped by client and currency. This is clearly distinguishable from siblings like report_payments_vs_invoiced, report_invoiced_by_period, and invoices_summary.

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?

Explicitly names two use cases ('aging reports and collections follow-up'), which gives the agent a solid selection signal. It does not name an alternative tool or a when-not-to-use condition, so it falls short of the top band.

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