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

Annotations already provide readOnlyHint=false, idempotentHint=true, and destructiveHint=false. The description adds valuable context: it reveals the write action ('writes a stored message and delivers it on the public Internet') and explains idempotency ('client_id makes retries safe'). This goes beyond the annotations by clarifying the external side effect and how to handle retries. No contradiction with annotations.

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 sentences with zero fluff. The primary action is front-loaded, the side effect is stated next, and the parameter guidance is compact. Every sentence earns its place.

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 7-parameter tool with no output schema, the description covers the core behavior, side effects, and key parameter semantics. It omits explicit return-value information, but that is not critical for a send operation. The description is sufficient for an agent to know how to call it correctly, though it could benefit from stating what the function returns (e.g., a message ID).

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 0%, so the description must compensate. It explains that 'text' and/or 'html' can be passed, attachments are optional, and 'client_id' ensures idempotency. It does not explicitly explain 'to', 'subject', or 'inbox_id', but these are intuitive from the context ('addresses in to' and 'from the Cooper inbox'). It covers the non-obvious parameters meaningfully.

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 description states a specific action ('Send an email from the Cooper inbox to the addresses in to') with a clear verb and resource. It also mentions content types and attachments, making it distinct from sibling tools like cooper_inject_inbound (which simulates inbound mail) and cooper_reply_task (which replies to tasks).

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?

The description clearly states what the tool does but does not explicitly contrast with alternatives or provide when-not-to-use guidance. For example, it does not mention that cooper_inject_inbound is for simulating inbound email, nor does it advise against using this tool for internal delivery. Usage context is implied but not explicitly framed against siblings.

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