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

Annotations already declare this is a non-read-only, non-destructive, non-idempotent mutation. The description adds real value beyond that by naming the resulting state ("payment recorded as unapplied") and warning against inferring settlement. It does not warn about duplicate submissions despite idempotentHint=false, which is a meaningful gap for a payment-recording tool.

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?

Short, front-loaded and the critical constraint (don't guess the invoice) sits before the effects line. The opening fragment "Money arrived." is atmospheric rather than informational, but it costs little.

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 6-parameter mutation with no output schema, the description covers the key postcondition and the main misuse risk. It could go further on duplicate handling and on how the unapplied balance is later settled, but the essential call-time knowledge is present.

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% and the property descriptions are unusually rich (cents units, ISO currency, currency-matching rule, value date). The description adds nothing parameter-specific beyond the applied/unapplied outcome, 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?

The description states a specific action on a specific resource (record an incoming payment) and draws a conceptual boundary against the settlement step, which maps onto the sibling solo_apply_payment. It never names that sibling outright, so an agent must infer the pairing rather than read it, which keeps it short of a 5.

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?

"Never guess which invoice a payment is for — unapplied is a valid, visible state. Ask, or leave it unapplied" is explicit when-to-use guidance with a stated fallback behavior. What's missing is a direct pointer to the alternative tool (solo_apply_payment) for the case where the invoice IS known.

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