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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds the non-obvious visibility constraint that only invoices created by the spend-key owner are returned, which is behavior the agent cannot get from annotations. It stops short of describing ordering or whether results are paginated beyond the limit.

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 short sentences, zero filler, with the scope constraint front-loaded and the routing hint second. Nothing could be removed without losing information.

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?

With an output schema present, return values need no explanation, and annotations plus full schema coverage handle safety and parameters. The description supplies exactly the missing pieces: ownership scoping and the get_invoice follow-up. Only result ordering is left unstated.

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 per-parameter descriptions and a status enum, so the schema does the heavy lifting and a 3 is the baseline. The description's "(open, paid, etc.)" adds only loose color and notably uses "open", which is not one of the enum values (pending/paid/expired/cancelled), creating mild ambiguity rather than clarity.

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 ("List invoices") plus the crucial scope qualifier "the spend-key owner created", and enumerates the statuses covered. An agent can distinguish it from get_invoice and create_invoice without opening any 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 prescribes the workflow: use this to find a publicId, then call get_invoice for details. It also names the related siblings, so the agent knows which tool to reach for at each step rather than inferring it.

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