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

Annotations already declare this is a non-read-only, non-idempotent, open-world mutation with no destructive effect. The description adds value beyond that: case-insensitive uniqueness, rename-anytime semantics, the hosted-identity prerequisite, and the returned data.handle/data.url. Consistent with annotations — no contradiction.

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-loads the action, then the format rules, then mutability, then return fields, then the prerequisite. Dense but every clause carries distinct information with 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?

An output schema exists, so return values need no elaboration, yet the description still names data.handle/data.url helpfully. With annotations covering the safety profile and the description covering constraints, prerequisite, and mutability, an agent has everything needed to call it correctly.

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 baseline is 3. The description still adds meaning the schema omits: the 'starting with a letter or digit' rule and 'unique ignoring case', which the schema's bare 'ASCII letters, digits, _ or -' does not convey. That genuine addition pushes it above baseline.

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+resource: 'Claim or rename your handle' and clarifies the handle is 'the name shown in place of your generated nickname.' This cleanly distinguishes it from siblings like create_identity, claim_identity, and whoami, which an agent can rule out without opening any schema.

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?

'Claim or rename' names both use cases, 'You may rename at any time' gives the cadence, and 'Needs a hosted identity (create_identity)' names the prerequisite and a sibling. It stops short of explicit when-not-to-use or a full alternative comparison, so it lands just under the top tier.

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