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

Annotations already cover the safety profile (readOnly, non-destructive, closed-world), so the bar is lower. The description adds real behavioral context: results may be detected patterns 'where available' or derived from settled invoice dates, and output is timing-only with no gain/loss figures. It doesn't state coverage limits or caveats on the derived fallback, but the added context is substantive.

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?

Three sentences, each earning its place: what it returns, when to use it, and what it deliberately excludes. The most important scoping detail (timing-only, derived fallback) is front-loaded with zero filler.

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?

An output schema exists, so return-value documentation is not required, and the description covers the fallback data source and the timing-only scope. Given a low-complexity read tool with fully documented optional params, this is nearly complete; only the boundary against sibling timing/driver tools is 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% with both optional filters fully documented (ISO 4217 pattern, entity_id from list_entities, omit-for-all semantics). The description's 'by counterparty and currency' maps to the params but adds no syntax or format detail beyond the schema, so baseline 3 applies.

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 ('Returns detected payment timing patterns') and resource, with the two dimensions that scope it (counterparty, currency) and a data-source fallback. It does not explicitly distinguish itself from near siblings like get_cashflow_timing or get_overdue_drivers, so an agent must infer the boundary.

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?

'Use for factual questions about who pays late or early' gives a clear trigger context, and 'Reports timing only, not realised gains or losses' sets a boundary on what questions it answers. No alternative tool is named for the adjacent cases, 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.