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

With no annotations, the description carries the full burden and does so well: nameplate is consumed on success, unknown/used/expired nameplates are deliberately indistinguishable (error behavior), the return payload is named (this side's key plus peer SPAKE2 message), and a hard security constraint is stated (the 5-char password must never reach the server).

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 tight sentences, front-loaded with the tool's role in the pairing flow, followed by argument rules, lifecycle, and error semantics — no filler. Slightly dense, but every clause carries operational 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?

No output schema exists, yet the description names the return values, the consumption side effect, and the indistinguishability of failure modes. For a security-sensitive pairing tool, nothing an agent needs to invoke it correctly 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 coverage is 100%, so the schema already documents both parameters and the 3-character nameplate format. The description goes beyond it by explaining why only 3 characters are sent and that the remaining code is a password that must stay client-side, adding real meaning to the nameplate argument.

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 (join the channel as the second half of pairing) and identifies the execution context (local client at channel.py). An agent can distinguish this from channel_open, which must be the first half of the pairing flow.

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 'second half of pairing' framing and the client-script reference make the when-to-use context clear, and the code-splitting rule (3 chars here, 5 chars never sent) is an actionable precondition. It stops short of explicitly naming channel_open as the required predecessor by tool name or stating when-not to call it.

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