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

With no annotations provided, the description carries the full burden of behavioral disclosure. It reveals side effects and defaults: signature appended automatically, message threads against a contact when contactId is passed, and messages leave from the oldest mailbox without accountId. These are meaningful behavioral traits beyond basic 'send an email' semantics, though it omits details like rate limits or error handling.

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 dense but every sentence earns its place: purpose, recipient syntax, body requirement, contact behavior, account selection, and signature note. It is front-loaded with the core action and immediately covers the most important parameter decisions. No filler or repetition exists.

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 12 parameters and no output schema or annotations, the description covers the critical decisions: recipient format, body requirements, merge tag handling, account selection, and signature behavior. It relies on the schema for details like cc/bcc and scheduling, which is acceptable since schema coverage is 100%. The picture is nearly complete, though error scenarios or expected return values are not described.

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, but the description adds value beyond parameter names. It clarifies that at least one of bodyHtml/bodyText is required, gives merge tag examples ({{first_name}}, {{cf.<field_key>}}), and explains that contactId does not pick the mailbox while fromEmail does not either. This helps an agent compose parameters correctly.

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 and resource: "Send an email from the user's connected email account." It clearly identifies the tool's action and adds concrete scope (recipient list, body formats, merge tags, account selection). It does not explicitly contrast against sibling tools like email_get_thread or email_list_threads, but the action is unambiguous.

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 provides clear usage context: when to pass contactId for merge tag resolution and threading, and when to call email_accounts_list and pass accountId to select a mailbox. It also states the default behavior when accountId is omitted. However, it does not explicitly mention when not to use this tool or compare it to alternatives, so it stops 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.