send_email

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

With no annotations present, the description carries the full behavioral burden and does disclose real traits the schema does not: suppressed and topic-opted-out recipients are silently skipped, and the call returns the email id. It still omits permission/domain verification requirements, error/partial-failure behavior, and rate limits, so it is not complete.

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 short sentences, front-loaded with the core action, and each sentence carries a distinct fact (what it does, suppression behavior, return value). No filler.

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 14-parameter write tool with no annotations it is only partially complete; noting the returned email id usefully compensates for the missing output schema, and the suppression rule is valuable, but constraints such as html/text being required together, domain verification, and 30-day scheduling limits are left entirely to the 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 coverage is 71%, so the schema already documents most parameters (notably the detailed idempotency_key and scheduled_at semantics). The description adds only the high-level meaning of scheduled_at; undocumented params like tags, headers, and attachment fields get no help from it. Baseline 3 is appropriate.

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?

Clear specific verb+resource ('Send a transactional email') with an explicit secondary mode ('or schedule it with scheduled_at'). However it does not distinguish itself from the very similar sibling send_email_batch, leaving the agent to infer the single-vs-batch boundary.

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 hints at scheduling usage via scheduled_at and implies the normal immediate-send path, but gives no when-to-use/when-not guidance and never names the alternative tools (send_email_batch for multiple sends, cancel_email to undo a scheduled one). Usage is implied rather than stated.

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