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

Adds substantial behavioral detail beyond the annotations: it does not enroll, start, or write delivery activity, but it does produce an external email side effect. It also shares retry guidance and required permissions. The idempotency-key note does not contradict idempotentHint=false because it only instructs how to retry, not that the underlying operation is idempotent.

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 core action in the first sentence, with every subsequent sentence adding distinct value: side-effect absence, external effect, retry behavior, permissions, and API reference. No wasted words or redundant restatements of the title.

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 an output schema present, return-value details are unnecessary. The description covers the tool's intended purpose, non-effects, external side effect, retry semantics, permissions, and documentation link, making it fully usable for a 3-parameter tool with a nested body.

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 100%, so the baseline is 3. The description adds meaning by tying 'five selected saved Sequence emails' to message_ids and 'explicit test address' to recipient, plus the idempotency_key retry instruction. It slightly underrepresents that message_ids can also be Automation step IDs, but the schema fills that gap.

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?

Uses a specific verb ('sends') plus a precise resource ('up to five selected saved Sequence emails') and a clear destination ('one explicit test address'). The explicit negations ('does not enroll a Subscriber, start the Sequence, or write delivery activity') distinguish it from real sending or enrollment tools.

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?

Provides clear context for when this tool is appropriate: testing sequence emails without enrolling subscribers or changing sequence/delivery state. It does not explicitly name alternatives like automations_send_test or broadcasts_send_test, so it falls short of a full 'use instead of X' guideline.

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