Send a message to a subagent

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

With no annotations provided, the description carries the burden of behavioral disclosure. It discloses queueing behavior, FIFO ordering, strict serialization, and the need to resume stopped/dead subagents, which goes well beyond the schema. It does not cover return values or failure behavior, but the core semantics are transparent.

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?

Two sentences, front-loaded with the purpose, followed by behavioral details and a prerequisite. Every sentence earns its place and there is no filler.

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 tool with no output schema and no annotations, the description covers the essential operational context: what it does, when messages are queued, serialization, and the resume prerequisite. It does not explicitly tell the agent to poll or wait for the result, but that is reasonable to infer from sibling tools.

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 schema already documents both parameters. The description adds useful context about the name parameter (subagent handle validity and resume requirement), but does not add substantial new semantics for either parameter beyond what the schema provides.

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 sends a follow-up prompt to a subagent, using a specific verb and resource. It distinguishes itself from spawning by saying 'follow-up', but it does not explicitly name sibling tools like interrupt or resume, so differentiation relies on context.

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: messages queue in FIFO order and are serialized per session, and stopped/dead subagents must be resumed first. It does not explicitly mention alternatives or when-not-to-use, but the queueing and prerequisite guidance is strong.

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