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

Goes well beyond the annotations: annotations only say readOnlyHint=false and destructiveHint=false, while the description discloses the authorization model (refused to the agent regardless of role), the real-world consequence ('money moves in their bank'), and the resulting state ('bill approved for payment'). It also makes clear the bill is not yet paid, which prevents a costly misinterpretation.

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?

Front-loaded with the core meaning and the refusal, which is the right order. It loses a point for redundancy: 'refused to you whatever your role' is stated twice in near-identical wording, which is wasted space in a short description.

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 human-only, three-parameter mutation with no output schema, this gives the agent everything it needs: what the action means, that it must not perform it, and the exact fallback (show purch_payables, ask the human). Nothing required to call or correctly avoid the tool is missing.

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%, so bill_id, pay_by, and note are already documented with examples and formats. The description only echoes the optional pay-by date and adds nothing about format or defaults beyond the schema. Baseline 3 is appropriate.

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 ('a person approves paying a bill'), names the optional parameter (pay by a date), and explicitly distinguishes the act from payment ('Approval is not payment: the money moves in their bank'). That distinction separates it from purch_record_bill_payment without opening either 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?

Explicitly says who may use it and who may not ('HUMAN-ONLY: this act is refused to you whatever your role'), then names the correct alternative workflow: show the bill via purch_payables and let the person approve in the app. There is no ambiguity about when to call this versus defer.

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