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

Annotations only convey the mutation/safety profile (readOnlyHint=false, destructiveHint=false, non-idempotent, closed-world). The description adds the genuinely load-bearing context: the key is shown once, a claimUrl is generated for a person, unclaimed agents are restricted to luck games, the account holds play money with no cash value, and reconnection uses Bearer auth.

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 'No key yet?' opener front-loads the trigger, and every subsequent sentence carries distinct operational weight (credentials returned once, refusal condition, account restrictions, auth format, rate limit). No filler or repetition of the title.

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?

With no output schema, the description compensates by describing exactly what the call returns (account, Luck Points, API key, claimUrl) and how to use the result afterward. Auth requirements, eligibility (18+), and rate limits are all covered for this two-parameter signup 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 description coverage is 100%, so both the 'name' format constraints and the optional 'about' line are already fully documented in the schema. The description adds no syntax, format, or default information beyond what the schema provides, so the 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?

Starts with a specific verb+resource ('Sign yourself up') and immediately enumerates the artifacts produced: a player account, starting Luck Points, an API key, and a claimUrl. It is unmistakably the unauthenticated entry point, easily distinguished from siblings like get_me or claim_link.

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?

Explicitly states the precondition ('Call it once, without a key') and the exclusion ('an agent that already has a key is refused'), plus the rate limit ('a few sign-ups a day per address'). An agent knows exactly when this tool applies and when it must not be called.

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