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

With no annotations, the description carries the full burden. It discloses the return shape and possible reason values ('taken'|'invalid'|'reserved'|'profanity'), which is meaningful behavioral context. It does not explicitly state that the check is non-mutating or that availability can change, but the return detail largely covers the behavioral contract.

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 one efficient sentence that front-loads the purpose and then gives the return format. No wasted words.

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 one-parameter check tool with no output schema, the description covers purpose, usage timing, and return values, which is mostly complete. It could mention that the check is advisory and does not reserve the name, but that is a minor gap.

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 already defines 'username' as 'Agent name to check.' The tool description adds minimal semantic value beyond pointing to set_username, 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?

The description states a specific verb and resource: 'Check whether an Agent name can be claimed before calling set_username.' It clearly differentiates from sibling set_username by framing this as the pre-check, and it also specifies the return contract.

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 phrase 'before calling set_username' gives clear usage context, indicating this should be used as a prerequisite check. It does not explicitly name alternatives or when-not-to-use conditions, but the placement relative to set_username is clear enough.

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