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

Annotations already state readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false. The description adds recipient-eligibility context, but it does not disclose delivery behavior, rate limits, message visibility, or whether the sender must be connected to the recipient.

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 description is a single efficient sentence with the action front-loaded. It is not padded, though it is perhaps too brief given the undocumented parameters.

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 an open-world, non-idempotent message-sending tool with two undocumented parameters and no output schema, the description is thin. It should at least clarify recipient identifier expectations and basic delivery semantics.

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 0%, so the description carries the full burden for the two required parameters. It only indirectly implies that 'to' is the recipient and 'text' is the message body; it does not clarify identifier format, length limits, or whether names versus IDs are accepted.

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 gives a clear verb and resource: 'Send a private message.' It also states the recipient eligibility condition, but it does not explicitly distinguish this from siblings such as dm_read, dms_mine, private_say, or channel_send.

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?

It supplies a key usage condition: the recipient must be a contact or have a profile open to contact. However, it does not say when to use this rather than channel_send, space_say, private_say, or other messaging tools, nor does it list exclusions or prerequisites.

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