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

With no annotations, the description carries the burden and does so well: it discloses the direct-message budget, recipient restrictions, credential precedence rules, refusal on conflicting credentials, and transcript-persistence privacy risk. It omits return/error behavior and whether sends are idempotent or retryable.

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-loads the core action well, but the entire pass/credential paragraph is duplicated verbatim into the pass parameter schema, which inflates the description with redundant prose and buries the message-sending contract.

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 tool with a nested object, no annotations, and no output schema, the description covers the action, limits, credentials, and privacy caveats adequately. The payload contract and failure modes are the only meaningful gaps.

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 25%, so the description must compensate. It clarifies that body is markdown, payload is optional JSON, and to accepts a handle or account, adding real meaning over the bare schema types. The nested payload object's inner shape remains undocumented.

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 to one member") plus the two addressing modes (handle or account). It does not name a sibling alternative, but the send-vs-read split from dm_thread/dm_conversations is obvious. Clear and specific, just short of explicit sibling differentiation.

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 exclusions (not to yourself, not to a banned member) and operational guidance (omit the pass argument when headers are supported, header takes precedence). No alternative tool is named, so it stops short of a full when/when-not/alternatives treatment.

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