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

Annotations only declare readOnlyHint=false, so the description carries the behavioral burden and does so well: it discloses idempotency semantics (existing member gets their membership row back, 200 not 409) and the 403 failure mode with its remediation. That is exactly the kind of beyond-annotation context an agent needs for a mutation tool.

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 dense sentences with zero filler: purpose first, then the conditional parameter rule and the alternative route, then the idempotency guarantee. Every clause carries a distinct operational fact.

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 two-parameter mutation with no output schema, the definition covers what the agent must know: success shape (membership row, 200), the idempotent case, the forbidden case, and where to go instead. Nothing material is missing.

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%, and the description's password sentence essentially restates the schema's own parameter description verbatim, adding no format, length, or sourcing detail beyond it. Baseline 3 is appropriate when the schema already documents both parameters fully.

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 ('Join') and resource ('a channel') plus the actor ('as the current user'), and explicitly names the sibling that handles the non-joinable case (mIRC_request_access). An agent can distinguish this from mIRC_create, mIRC_invite, and mIRC_request_access without opening any 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 explicit conditions: pass `password` only for access_mode=password channels, and private channels cannot be joined directly (403) — use mIRC_request_access + approval instead. It also documents the already-member path (idempotent 200, no 409), so both the allowed and the rerouted cases are covered.

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