send_message

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

No annotations, so the description carries the full burden. It does usefully disclose the transport routing (native UDS/tmux and Codex Desktop IPC preferred, otherwise headless CLI resumes the exact session) and that the message is always queued in the magents mailbox. It omits whether the call blocks for delivery, what happens if `to` is unknown, and any auth/permission requirements.

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?

Front-loaded with the core action, then routing and delivery semantics in two supporting sentences. The eight-backend enumeration is slightly listy but it earns its place by defining valid targets; no wasted 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 2-param, no-annotation, no-output-schema tool, the description covers purpose, routing, and durable queueing. Missing pieces are the failure/unknown-target behavior and the acknowledgement or return semantics, which the absence of an output schema leaves unexplained.

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 50% (`to` documented, `message` bare). The description confirms `to` must reference an existing chat but adds no format detail, alias resolution rules, or constraints for either parameter beyond what the schema already states.

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?

Specific verb+resource: 'Send a message into an existing ... chat,' and it enumerates the supported agent backends, which scopes the tool well. It does not, however, differentiate from the sibling `reply` tool, so an agent cannot tell the two apart from the descriptions alone.

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?

'Existing ... chat' implies the target session must already exist (contrast spawn_session), and the routing preference hints at when a native path is used. But there is no explicit when-to-use vs `reply`, `await_reply`, or `inbox`, and no stated failure condition.

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