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

With no annotations, the description carries the full burden, and it does disclose meaningful behavior: the PayNow failure mode and its error code, plus the merchant-key auth requirement. However, it says nothing about partial-refund semantics (amountMinor), what revokeAccess actually does, or whether a refund is reversible, which are exactly the mutation traits an agent needs.

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 front-loaded sentences with no filler: what it does, the refusal case, then the auth prerequisite. Every sentence carries information an agent needs.

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 money-moving mutation with no annotations, no output schema, and zero schema description coverage, this is thin. It never explains what a successful refund returns, how partial refunds behave, or what revokeAccess changes, so an agent could invoke it correctly only by guessing at its most consequential fields.

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 0% and all five parameters (reason, reference, amountMinor, revokeAccess, idempotencyKey) are undocumented in the schema. The description compensates for none of them; the only hint is the merchant-key auth note, which isn't even a parameter. Partial amounts and access revocation remain entirely undefined.

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?

Specific verb+resource: 'Refund a settled payment through its provider.' It scopes the operation further (settled only, PayPal/test key) and explicitly names the case it refuses (PayNow -> REFUND_UNSUPPORTED). No sibling in the list performs refunds, so an agent can route here unambiguously.

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?

Gives a clear precondition (payment must be settled) and a clear exclusion (PayNow payments are refused, not recorded). It also notes the merchant-key requirement. It doesn't point to an alternative for the unsupported case, but no sibling offers one, so nothing essential is missing.

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