Compose and send an email

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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It states the tool sends an email, which implies a side effect, but it does not disclose whether sending is irreversible, whether it requires authentication beyond the configured account, whether it validates recipients, or what happens on failure. It also does not mention that both text and html can be provided together or how the email client handles that. For a mutating tool with zero annotation coverage, this is a significant gap.

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 description is a single sentence that front-loads the main action and resource, then adds the body-format detail. It is concise and every word earns its place. It could arguably include more behavioral context, but for its length it is well-structured.

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?

Given that this is a mutating tool with no annotations and no output schema, the description is incomplete. It does not explain return values, error behavior, sending semantics (e.g., whether it actually sends immediately), or any constraints like attachment support. The schema covers parameters, but the description leaves out important operational context an agent would need to invoke the tool correctly and anticipate consequences.

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 all 8 parameters. The description adds the context that the body can be plain text and/or HTML, which maps to the text and html parameters, but it does not add meaning beyond the schema for the other parameters. Baseline 3 is appropriate because the schema does the heavy lifting.

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 verb ('Compose and send'), a resource ('a new email'), and the source account ('configured Yahoo Mail account'). It also mentions the two body formats (plain text and/or HTML), which distinguishes it from sibling tools like list_messages or get_message. The title reinforces the same action, so an agent can tell what this tool does without opening the schema.

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 implies the tool is for sending new emails and mentions the configured account, which gives some context. However, it does not explicitly state when to use this tool versus alternatives, nor does it mention exclusions or prerequisites (e.g., that it cannot be used to draft, schedule, or send from other accounts). The sibling list shows other email operations, but the description itself does not route the agent to them.

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