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

Annotations only declare readOnlyHint=false, so the description carries most of the burden and does so: the message is never encrypted, this path is mandatory for fleet/King traffic, and the choice is permanent. It does not describe what is returned or whether delivery can be revoked or fails, which keeps it from a 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?

The mandatory-routing rule is front-loaded and the alternative tool is mentioned last, which is the right ordering. It repeats the unencrypted idea twice ('plain text, never encrypted' then 'in the clear'), a minor redundancy in an otherwise dense passage.

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 4-parameter mutation with no output schema, the description covers routing policy, recipient id sourcing, permanence, and thread behavior. The main gap is that it never says what a successful send returns (e.g., a message id) or how failures surface.

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 description restates that `to` is a mosadd identity_id found via mDM_list_contacts and that thread_label creates a named thread, which is essentially the same information the schema already provides, adding little beyond it.

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 and resource (send a direct message) plus the defining constraint: plain text, never encrypted. It explicitly separates itself from the sibling mDM_send by naming the condition under which mDM_send would take the same path, so an agent can distinguish the two without opening either 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 concrete routing rules: every agent line writing to the King, to another line, or to itself must use this tool, and the choice is permanent. It also names mDM_list_contacts as the prerequisite for obtaining `to`. It stops short of an explicit 'use mDM_send instead when no fleet line is a party', leaving that inference to the reader.

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