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

Annotations already flag a non-read-only, open-world operation, and the description adds real value beyond them: it discloses the per-call confirmation requirement (and that it can be disabled), that the action 'reaches other people', and the API-key/access prerequisite. It stops short of describing rate limits or how the send resolves on failure.

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 in the first sentence, followed by effect and safety/confirmation notes. The trailing confirmation and API-key sentences read as boilerplate and are mildly redundant with each other, but nothing is badly buried.

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 no output schema, the description carries the return-behavior burden and does so reasonably (invoice marked sent). It covers effect, confirmation, and auth across six well-documented parameters, leaving only failure/error behavior unspecified.

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 baseline is 3. The description largely restates schema content ('main customer of the job', 'addresses you add' for cc) rather than adding new meaning such as format constraints or precedence rules among recipients.

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: 'Email the invoice of a job to the customer.' This is clearly distinguishable from siblings like kickserv_generate_invoice (creates) and kickserv_send_estimate (different document), so an agent can route 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?

Explains the effect ('The invoice then shows as sent on the Invoices page') and the default-confirmation behavior, giving clear context for when this tool applies. It does not explicitly name alternatives such as generate_invoice or list_invoices, so exclusion guidance is left implicit.

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