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

Annotations declare a non-destructive write (readOnlyHint=false, destructiveHint=false, openWorldHint=true), and the description adds substantial context beyond them: a permission-error failure mode, the fact that approving does not trigger payment, default per-call confirmation, and that the action reaches other people so the user should be consulted. That is rich on top of what annotations already supply.

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 action and safety caveat, and every statement carries meaning. However, it opens with redundant restatement ('Approve... on the Approve Bills for Payment form. Approves one bill on the Approve Bills for Payment form...'), and the confirmation guidance is split across two sentences ('you confirm each call' and 'confirm with the user before each call').

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 one-parameter mutation with no output schema and annotations covering safety, the description is nearly complete: it covers permission requirements, non-payment semantics, and confirmation policy. The only mild gap is that it doesn't explain the effect on the bill's subsequent state beyond 'so it can be paid'.

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 the single required parameter (reference_nbr) is already fully documented, including its source ('from list_invoices or list_bills'). The description adds nothing beyond the schema, so the 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 (approve) and resource (an open bill for payment) and scopes it to a single bill on the Approve Bills for Payment form. An agent can distinguish it from list_bills_for_payment_approval or release_ap_bill without opening a 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?

The description clarifies the boundary that 'approving does not pay the bill', which helps distinguish it from record-payment siblings, and notes the permission-error condition. It stops short of naming a specific alternative or when-not-to-use, so it's clear context but not full routing guidance.

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