open_dm

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

Annotations declare readOnlyHint=false and idempotentHint=true; the description usefully explains what that idempotency means in practice ('or returns the existing one'), which is real context beyond the boolean. It still omits permission requirements and whether display-name lookup can fail on ambiguity, so it isn't fully transparent.

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?

Two tight sentences with zero filler: the first states the action and its idempotent edge case, the second states the downstream handoff. The essential fact (what is returned) is front-loaded.

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?

With no output schema, the description correctly compensates by naming the return value (channelId) and how to use it. Siblings and annotations cover most of the rest, though failure modes (non-unique display name, unknown peer) are left unstated.

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 100% and the schema already documents 'peer' as UUID or unique display name. The description adds only the parenthetical '(when unique)', which restates the schema's 'unique' qualifier rather than adding new semantics. Baseline 3 is correct when the schema carries the parameter meaning.

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 — 'Opens a 1:1 direct message channel with another account' — and clarifies the idempotent return-existing behavior. The '1:1 direct message' scope implicitly separates it from the channel-oriented siblings (create_channel, create_server), but it never names an alternative outright.

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 forward guidance on consumption: 'Use the returned channelId with send/read,' which routes the agent to the correct follow-up tools. It does not state a when-not condition or name the sibling it supersedes (e.g., create_channel for multi-party), so it stops short of full routing guidance.

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