send_email_message

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 correctly conveys that the tool only replies and does not start new threads, and highlights the mutual exclusivity of leadId and leadEmail. However, it does not mention authentication requirements, rate limits, or error handling (e.g., what happens if the thread does not exist), leaving some gaps in transparency.

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 two sentences long, front-loaded with the primary purpose, and includes all critical constraints without extraneous words. Every sentence provides essential information, making it highly efficient for an AI agent to parse.

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 tool with 9 parameters, 2 required, nested objects, and no output schema, the description covers the core behavior (reply-only), the two reply methods, and the leadId/leadEmail constraint. The only minor gap is the subject parameter: it is described as 'for new threads' but the tool cannot create new threads, so a brief note on when subject might be used (e.g., if the reply becomes a new thread in some cases) would improve completeness.

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?

The input schema has 100% coverage, with descriptions for all parameters. The description adds value beyond the schema by explaining the reply mechanism (replyToMessageId from get_conversation_messages, replyInLastThread) and the 'either leadId or leadEmail' constraint. It also clarifies that subject is for new threads, though the tool cannot initiate new threads – a slight inconsistency but still informative.

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 clearly states it is for replying to an existing email thread with a lead, explicitly distinguishing from initiating new conversations. It uses specific verbs ('Reply to') and identifies the resource ('email thread with a lead'), which differentiates it from sibling tools like send_linkedin_message or get_conversation_messages.

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 explicit guidance on when to use this tool (to reply to an existing thread) and when not to use it (cannot initiate new conversations). It names alternative parameters (replyToMessageId or replyInLastThread) and specifies the leadId/leadEmail constraint, offering clear context for selection.

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