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

Annotations already declare readOnly, idempotent, non-destructive and open-world, and the description adds real context beyond them: the free tier (10 calls/day), the paid path ($0.001/call) and the two auth mechanisms (x402 payment in params._meta or HTTP header, X-API-Key credits). It stops short of saying whether invalid payees cause an error versus only being flagged in the result, but the cost/auth disclosure is genuinely useful for an agent.

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 compact sentences: the functional statement comes first, the commercial/auth detail second. Nothing is redundant, and the '[served by tools.moneytools.dev]' tag is a small, identifiable provenance note rather than filler in the body of the definition.

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?

An output schema exists and annotations cover the safety profile, so the description need not explain return values. It covers inputs, what is validated, cost, and authentication; the only meaningful gap is clarifying whether the check mutates or blocks anything versus purely reporting, which 'check' implies but doesn't state outright.

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 coverage is 100% with descriptions and examples on all three parameters, so the schema does the heavy lifting and the baseline of 3 applies. The description adds only light semantic hints — that payees must be valid/non-zero and that per-payment limits apply — without explaining format, ordering, or how maxPerPaymentUsd interacts with budgetUsd when omitted.

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 ('Check a planned list of agent payments against a USD budget and per-payment limit') and enumerates exactly what the check surfaces: invalid/zero payees, duplicates, over-budget. This is plainly distinct from siblings like payment_receipt_verify or card_number_check, so an agent can select it 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?

Usage is implied by 'planned list' — i.e. pre-flight validation before sending payments — but the description never says when not to use it or points to an alternative (e.g. receipt verification after the fact). The pricing paragraph is about billing, not about choosing this tool over another.

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