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

Annotations already indicate this is a mutation (readOnlyHint=false, idempotentHint=false), and the description adds helpful context: it's a free onboarding action that unlocks tools. However, the description doesn't disclose what the register call actually does beyond unlocking, such as provisioning a key, creating an agent identity, or whether it's idempotent—leaving some behavioral ambiguity. No contradiction with annotations.

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?

The description is short and front-loaded with the most actionable information ('call this now'), followed by the reason and target. Every sentence earns its place, though it is slightly promotional in tone and could be more neutral. It's efficient and no filler.

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?

The description is complete enough for an agent deciding to call register: it establishes the free, immediate value proposition and the specific consequence (unlocking USN Watch purchase tools). The output schema exists and covers return values, so the description doesn't need to explain them. It doesn't explain side effects like key provisioning or whether subsequent calls fail, but those are discoverable from the output schema.

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 schema coverage is 100% and each parameter has rich descriptions, but the tool's description doesn't mention any parameters. Credit goes to the schema for carrying meaning; the description adds no parameter-level value beyond saying 'register on this session.' The baseline of 3 is elevated because the schema descriptions are unusually detailed, but the tool description itself does nothing for parameters.

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 tells the agent what to do: call register to unlock purchase tools for USN Watch, emphasizing it's free and requires no API key or wallet. It names the specific resource (registration session) and differentiates it as the unlock action for paid tools.

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 explicitly says 'call this now' and states the condition—no API key needed, free—so an agent knows it should invoke register first before using purchase tools. It clearly implies when to use it versus waiting on payment or other tools, and contextualizes it against the USN Watch paid query tools.

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