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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds that this is a GET endpoint and sketches the payload (codes plus names), which partially compensates for the absent output schema, but it says nothing about ordering, completeness of the list, or whether codes are firm-specific.

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 short sentences, front-loaded with what the caller gets. The trailing raw endpoint path 'GET /invoices/payment-methods' is marginally useful for orientation but borders on 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?

For a zero-required-param reference lister with no output schema, the description conveys the essential return content (codes and names) and the schema covers the one optional parameter. Missing only minor details such as ordering or whether the list is static across firms.

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%: the single optional 'language' enum param is fully documented in the schema, including the bg default and the fallback behavior. The description adds nothing beyond that, so the 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?

The description identifies the exact resource: the payment-method codes a record accepts, with their human-readable names, and gives examples (card, card, cash). That is enough to distinguish it from sibling enum-lookup tools like list_invoice_items or list_vat_exemption_reasons, though it never explicitly frames the operation as 'list' or contrasts with those siblings.

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?

There is no explicit when-to-use statement or named alternative. Usage is only implied by the phrase 'the payment method codes a document accepts', which suggests it is a reference lookup for populating invoice/payment fields. An agent can infer the context but must do the work itself.

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