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

Annotations only declare readOnly=false and idempotent=false; the description adds substantial non-obvious behavior: NON-BLOCKING execution, a confirm gate because the device goes on a human's head, automatic cue display in the app, the Pro-plan requirement, and a specific 403 policy for local X-MCP-Key principals. These are precisely the traits annotations cannot express.

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 sentences, front-loaded with the purpose and the critical non-blocking/confirm facts before the plan-gating detail. Dense but every clause carries information; minor line-broken parentheticals add slight reading friction.

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?

An output schema exists and annotations cover the safety profile, so the description only needs to add the operational context it does: non-blocking semantics, the confirm requirement, the follow-up polling step, and the authorization gate. For a 14-parameter, policy-gated session tool, nothing an agent needs before invoking 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 each parameter (confirm, paradigm, classes, connection selectors, device_type, trials_per_class) is fully documented in the schema itself. The description echoes the confirm-gating but adds no new syntactic or constraint detail beyond what the schema already provides, so the baseline of 3 applies.

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 ('Start a guided subject calibration session') and clearly distinguishes itself from the sibling lifecycle tools (calibration.status/pause/resume/train). An agent knows immediately this begins a session rather than querying or adjusting one.

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 clear operational guidance: it is non-blocking, the app displays cues automatically, and the caller should follow up by polling calibration.status. It also states a hard prerequisite (Pro plan / hosted token). It does not explicitly contrast with calibration.train or state when-not to use it, keeping it short of a 5.

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