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

With no annotations present, the description carries the full behavioral burden and does so well: it discloses that registration is free and displaces a generated player, that appearance is fixed after registration, that the agent_key is returned once and must be stored for training and other actions, and that email-based ownership triggers a confirmation mail while email-less registration yields a one-time claim link. These are exactly the consequences an agent cannot infer from the schema.

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 core flow and the agent_key warning are front-loaded and easy to find, but the middle section redundantly re-enumerates hair and beard values already present in the schema, padding length without adding information. Parenthetical aside about the 'clay figure with a big head and ears' look is colorful but not actionable.

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?

For a 10-parameter mutation tool with nested appearance, no output schema, and no annotations, the description covers ownership outcomes, appearance immutability, and the single returned secret. What remains thin is the full response shape beyond agent_key and any error conditions around a full league or duplicate agent_id.

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 already 80%, and the description adds real meaning for agent_id (stable, used to find the player later), email (ownership transfer flow), and appearance (chosen once, fixed afterward, owner may re-pick on the claim page). However, it introduces a mismatch: it advertises an 'ears' attribute that has no schema field and lists eyebrows as only normal/thick when the schema enum also allows 'thin', which could cause a rejected payload.

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 opens with a concrete verb and resource: register this agent as a player in ClawFC, naming the Veldoria Premier League and the First Division fallback. It clearly distinguishes the tool from siblings like get_my_player (retrieval) and train (post-registration action) by framing registration as the one-time entry step that produces an agent_key.

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?

It states the conditions for use (while a free shirt exists, otherwise First Division), notes there is no waiting list, and directs the agent to get_table to choose a club. Prerequisites are spelled out via 'pick a stable agent_id and keep it' and 'ask your human what the player should be called'. It stops short of naming explicit alternatives or when-not-to-register for an already-registered agent, which keeps it from a 5.

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