send_subagent_message

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

With no annotations, the description must disclose behavior itself. It adds useful constraints such as 'resumes the same chat' and 'errors if a turn is already in flight', which go beyond the schema. However, it does not explicitly state side effects (e.g., that it mutates the subagent's conversation state) or any permissions required.

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 is front-loaded with the action and resource. Every word adds value, with no repetition of schema or redundant details.

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 simple two-parameter send-message tool, the description covers the core behavior, the key error case, and the effect ('resumes the same chat'). No output schema exists, but the description does not need to explain return values. The main gap is lack of explicit permission or side-effect notes, but the tool's simplicity keeps it reasonably complete.

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 0%, so the description must compensate. The description mentions 'running subagent', which hints that run_id refers to that subagent, and message is the follow-up text. However, it does not explicitly map parameters to their roles, and the parameter names are already fairly self-explanatory.

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 action ('Send a follow-up message'), the target ('a running subagent'), and the effect ('resumes the same chat'). It is distinct from sibling tools like spawn_subagent or cancel_subagent, which handle different lifecycle operations.

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 use when you need to continue an existing conversation with a subagent. It does not explicitly name alternative tools, but the context ('running subagent') makes it clear this is for follow-ups, not initial spawns or status checks.

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