pi_send

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

With no annotations provided, the description carries the full burden, and it delivers. It discloses the async behavior ('Returns immediately'), where the effect surfaces ('pi's reaction appears in the answer of the pi/pi_reply call still waiting on that turn'), and the transport/reachability constraint. This is exactly the kind of non-obvious behavioral context an agent needs beyond the schema.

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?

Four dense sentences with zero waste. The core action is front-loaded, followed by constraints, behavioral timing, and a helpful pointer to pi_running. Every sentence earns its place and no information is duplicated from the schema.

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?

Despite having no annotations and no output schema, the description covers the essential context: transport constraint, timing semantics, where the result appears, sibling differentiation, and session discovery. The only minor gap is the exact return value of pi_send itself (an ack?) and behavior on an invalid or unknown session id, but these are small omissions for an otherwise complete definition.

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 description coverage is 100%, so the baseline is 3: the schema already documents each parameter's meaning, including the command enum behavior and message requirements. The description adds marginal value by framing session as a currently executing turn and pointing to pi_running, but it does not meaningfully augment the parameter docs.

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 opens with a specific verb and resource: 'Deliver a message into a pi turn that is executing right now.' It explicitly distinguishes the tool from pi_reply ('a session that already finished takes pi_reply, not pi_send'), so an agent can tell them apart instantly. The scope is precise — only live turns on 'rpc' transport.

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?

This is exemplary routing guidance. It states the exact precondition ('Works only on runs started with transport 'rpc''), a negative exclusion ('print' runs cannot be reached), and names the alternative tool for the finished-session case (pi_reply). It also points to pi_running for discovering reachable sessions. Nothing is left to inference.

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