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

Annotations already declare readOnlyHint=false, openWorldHint=true and destructiveHint=false, so the safety profile is covered; the description still adds real value beyond that by disclosing the external recipient effect, the per-call confirmation default, and the Cotlet API key requirement. It does not explain delivery failures or duplicate-send behavior, keeping it below a 5.

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 leading 'Houzz Pro:' prefix duplicates the title, and sentences two and three restate the same idea ('Email an estimate or invoice to the client... Emails an estimate or invoice to the client, who can open it on...'). The critical recipient/confirmation facts are present but padded with redundancy.

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 mutating, externally visible send tool with no output schema this is nearly complete: recipient reach, confirmation expectation, auth prerequisite and the irreversible lock behavior of issue_on_send are all stated. Only the outcome of the send (success/failure signal) is left unaddressed, which is acceptable without an output schema.

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 message, document_id and issue_on_send. The description restates issue_on_send ('locks the invoice when it is sent') but adds no syntax, format or defaulting detail beyond the schema, so baseline 3 applies.

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 first sentence names a specific verb (Email) and resource (an estimate or invoice) plus the recipient outcome (view, approve, pay online). An agent can distinguish this from sibling create_estimate/create_invoice/list_invoices without opening the schema, since those create or read documents rather than send them.

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 operative conditions: 'By default you confirm each call; you can switch that off,' and 'confirm with the user before each call' because it 'Reaches other people.' However, it never routes the agent among alternatives (e.g., when to send vs. simply create or list a document), so usage is implied rather than resolved against siblings.

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