Send a message in a conversation thread

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

With only an openWorldHint annotation (which gives no safety/behavior info), the description carries the burden of behavioral disclosure. It explains important fallback behavior: missing channel_id/channel_account_id are taken from the thread, missing recipients are derived from the latest incoming message, and sender_actor_id defaults to HUBSPOT_DEFAULT_SENDER_ACTOR_ID. It also spells out field precedence and the mode='get_request_schema' capability, which goes well beyond the schema. It doesn't mention side effects or permissions, but for a message-sending tool this is substantial 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 dense but well-structured, front-loading the core purpose in the first clause. It is a few long sentences, but each clause carries unique information about delivery, internal notes, request_body, fallbacks, and schema inspection. A bit of trimming could improve readability, but it's not padded.

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 12-parameter tool with no output schema and minimal annotations, the description is highly complete. It explains the central execution flow, alternative invocation modes, parameter precedence, and default behaviors. It doesn't describe the return value, but the absence of an output schema is offset by the detailed operational guidance. It could be more explicit about what happens after a message is sent, but overall it is sufficient for safe invocation.

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 meaningful parameter semantics beyond the schema: 'typed fields win on conflict' between typed fields and request_body, and it clarifies default derivation for channel_id, channel_account_id, recipients, and sender_actor_id. This helps the agent understand how parameters interact and what will happen if they are omitted.

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 the tool's purpose: 'Send a new message on an existing conversation thread — delivered to the customer on the thread's channel.' It names the resource (conversation thread), the action (send), and distinguishes it from sibling tools like RetrieveThreadMessage or UpdateConversationThread. It also adds nuance by explaining that message_type=COMMENT is for internal notes, making the purpose even more precise.

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 gives solid context for when to use the tool: 'on an existing conversation thread' and 'delivered to the customer.' It also clarifies a key decision point with 'set message_type=COMMENT for an internal note instead.' However, it does not explicitly name sibling alternatives or provide when-not-to-use guidance, 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.