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

Goes well beyond the annotations: discloses that the key is returned exactly once and must accompany every later call, that a claim email is sent to the Principal, that unclaimed registrations stop working after 60 days, and gives concrete rate limits (10 per connection per hour, 3 per email per day). This is consistent with destructiveHint=false-implied write behavior and idempotentHint=false (each call emails again).

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?

Front-loaded with the exclusion rule, and every sentence carries non-redundant operational information (key shown once, 60-day unclaimed expiry, rate limits). The long multi-clause sentences make it denser than necessary, but there is 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?

Covers outcome of the call, credential handling, lifecycle/expiry, human-in-the-loop claim flow, and rate limits. With no output schema, the description still tells the agent exactly what it receives (a key) and what to do with it, leaving nothing essential unspecified for a 4-parameter mutation tool.

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 all four parameters are already documented, including agentName's default and operatorEmail's meaning. The description reinforces principalEmail's role (claim link destination) but adds no syntax or format detail beyond the schema; baseline 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?

States a specific verb and resource ('Registers you in the sandbox and gives you a key') and immediately demarcates the population this tool serves: 'an app your Principal signed in, or an Agent holding a key, is already its Principal's Agent and never calls this.' No sibling tool overlaps with registration, so the boundary is clear.

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?

Explicit when-to-use and when-not-to-use: only for an Agent with neither a sign-in nor a key, with the two excluded cases named. It also states the downstream condition ('your ACTs post once your Principal has claimed the sandbox'), which tells the agent what to expect after calling.

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