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

Annotations already declare readOnlyHint and openWorldHint; the description builds on that by revealing important non-obvious behaviors: amounts are in the linked invoice's currency, invoiceId/invoiceNumber appear only when applied to an invoice (not credit notes/prepayments/overpayments), and results echo applied filters. This goes beyond the 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 long but every sentence earns its place: purpose, alternative, currency caveat, invoiceId behavior, pagination handling, and filter echo. It is logically ordered and front-loaded with the core action before the caveats.

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 shoulders the burden of explaining return behavior, and it covers the essentials: pagination limit, pageCount guidance, currency semantics, and when invoiceId/invoiceNumber are present. An agent has everything needed to call this tool and interpret its results correctly.

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%, so the schema already documents every parameter thoroughly. The description adds a useful high-level summary of the filter options and inclusive date semantics, but most parameter detail remains in the schema; this is adequate without pushing above baseline.

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 payments already recorded in Xero'), then scopes it precisely: current organisation, optional filters for status, invoice, and date range. It also distinguishes itself from create_xero_payment, so an agent can tell them apart without opening the schema.

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 says this is read-only and nothing is created or changed, and names the sibling to use instead (create_xero_payment). It also gives operational guidance such as relaying pagination state and echoing appliedFilters rather than assuming completeness.

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