create_direct_channel

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

The description aligns with the idempotentHint annotation by stating 'Returns an existing DM channel if one already exists.' It adds behavioral context beyond annotations, clarifying the tool is non-destructive and suitable for private messaging.

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?

Three concise sentences front-loaded with the primary purpose, followed by key behaviors and usage guidance. No redundant information.

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?

Given the simple input schema (2 params), annotations (idempotent, non-destructive), and output schema presence, the description fully covers the tool's purpose, idempotency, and next-step guidance (use post_message).

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?

The input schema already provides 100% coverage with clear descriptions for both user IDs, including examples. The tool description adds no additional parameter semantics beyond what the schema provides, so baseline score of 3 is appropriate.

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 clearly states the tool creates a direct message channel between two users and distinguishes itself from siblings like 'create_channel' by specifying the DM nature and the idempotent behavior of returning an existing channel.

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?

The description tells when to use it (to get a channel ID for private messages) and implicitly guides not to use it when a channel already exists by mentioning the return of existing DMs. It could explicitly contrast with sibling tools but is still effective.

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