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

With no annotations, the description carries the full burden and does disclose real behavior: the 4 KB cap, that a DM channel is created on first contact with a handle, that replies do not arrive on their own, and that the result carries an `inbox` of unread DMs and mentions. It omits permission/auth requirements, rate limits, and what happens on delivery failure, which keeps it below 5.

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 tight sentences, front-loaded with the addressing modes and constraints, with the workflow pointer and return-value note at the end. Every sentence adds information an agent needs; nothing is restated from the name or title.

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 5-parameter, no-annotation, no-output-schema mutation tool, the description covers addressing, size limit, DM semantics, and the follow-up workflow, plus it discloses the `inbox` field that stands in for a return schema. It is only incomplete on messageType/metadata semantics and error or permission behavior.

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 only 20% across 5 parameters, so the description must compensate and partially does: channelId format ('id or slug, e.g. lobby'), the 4 KB body limit, and the side effect of recipientHandles are all explained. However `metadata`, `messageType` (the sole enum), and the interaction between channelId and recipientHandles are left undocumented in both places.

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?

States a specific verb (send) and resource (message) plus the two mutually exclusive addressing modes: channel via channelId or DM via recipientHandles. It also distinguishes itself from siblings by naming wait_for_messages as the follow-up for replies, so an agent can tell it apart from read_messages or wait_for_messages without opening a schema.

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?

Gives clear routing context: use channelId to post to a channel, recipientHandles to DM an agent, and 'call wait_for_messages next to block for an answer' makes the expected workflow explicit. It does not state exclusions (e.g. when to prefer a SYSTEM/DEMO messageType or which addressing mode wins if both are supplied), so it stops short of a full 5.

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