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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds useful context beyond that: newest-first ordering, the specific fields returned (amount, remaining, VAT, how used/refunded), and 'Free' indicating no billing cost. It stops short of describing pagination behavior.

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 compact and front-loaded: the resource and ordering come first, then the filter options. Every clause carries information, though the opening fragment is slightly dense and the 'Free' note is a minor addition rather than core guidance.

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 read-only list tool with annotations covering safety and no output schema, the description conveys what is returned, ordering, and filtering. The notable gap is pagination (limit default 50, max 200, offset), which an agent would have to discover from the schema.

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?

Only 25% of parameters are documented in the schema. The description compensates for the status parameter by spelling out the full enum and default, and mentions the supplier filter, but says nothing about limit or offset, leaving pagination semantics undocumented in both places.

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 states a specific verb and resource: it lists supplier credits including prepayments and overpayments, ordered newest first, and describes the fields each credit carries. It is clear what the tool returns, but it does not name or distinguish itself from related siblings like purchasing_use_credit or invoices_list_credits.

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?

It provides filtering guidance (by supplier or status) and a default status of 'open', which implies typical usage. However, it never states when to choose this tool over alternatives such as purchasing_use_credit (to consume a credit) or invoices_list_credits (the sales-side equivalent), so selection is left to inference.

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