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

Annotations already disclose non-read-only, non-idempotent, open-world behavior; the description adds the crucial safety fact that mail never reaches owners and that explicit user confirmation is required. It stops short of covering quota/cost impact or what a successful send returns.

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?

Three tight sentences; the what/who lands first, then the safety boundary, then the confirmation requirement. Nothing redundant.

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 full schema coverage and annotations present, and no output schema to explain, the description covers what an agent needs to call this safely. Only minor gaps remain: no guidance on what a returned success/failure looks like or on repeated test sends.

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 all four parameters are documented at the field level. The description restates the owner-data-vs-sample-data choice and the sender origin, but adds no syntax or format detail beyond the schema — baseline 3.

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 (send), resource (email template), destination (user's own account email), and data source (sample or owner data). The line 'Never goes to owners' crisply separates it from real-send tools like spur_send_letters and from preview tools like spur_preview_message_template.

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?

Gives clear context — use it to verify a template in a real inbox — and mandates confirming with the user first. It doesn't explicitly name the preview siblings or state when NOT to use it versus them, which keeps it short of a 5.

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