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

The description adds extensive behavioral detail beyond the annotations: it explains the state change (draft to Sent, balance increase, portal visibility, reminder counting), that a Sent invoice can be re-sent, template effects, conditional late fees, confirmation requirements, and API key scoping. It is consistent with the annotations (write, open-world, non-destructive) and discloses side effects and auth needs clearly.

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?

The description is front-loaded and covers important points, but it contains redundancy (repeating how contacts receive the invoice and listing template options already in the schema). It could be tightened 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?

Given the lack of an output schema, the description still explains the return value ('returns who got it'), the state changes, auth requirements, and user-confirmation expectations. It is thorough enough for an agent to invoke the tool correctly.

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 schema already documents all three parameters thoroughly. The description largely repeats schema content, such as the template enum and default, without adding new semantic meaning beyond what the schema provides.

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 clearly states a specific verb (email) and resource (invoice or reminder) and distinguishes from create_invoice by describing the sending/state-transition behavior. However, it does not explicitly name or contrast with any sibling tool (e.g., send_quote), so it stops short of the top score.

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?

It gives clear context for when to use the tool: to email an invoice or a reminder, including that a draft becomes Sent and a Sent invoice can be sent again. It also provides operational guidance about confirmation and API key requirements, but it does not discuss alternative tools or when not to use this one.

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