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

Annotations only say it is not read-only, is idempotent, and is non-destructive; the description adds the actual side effect that matters — the name is marked as taken for check_username_available for fifteen minutes, but direct signups are not blocked, no account is created, and nothing is sent. This is exactly the extra behavioral context annotations cannot carry, and it does not contradict them (the reservation is a real mutation, consistent with readOnlyHint=false).

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?

Five short sentences, front-loaded with what the tool returns and who consumes it, followed by the scope disclaimers. Every sentence carries distinct information (return value, recipient, no account, reservation window, nothing sent) with no repetition.

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 only one fully-described parameter and an output schema available, the description need not explain return values, and it spends its budget instead on the non-obvious behavioral boundaries. Nothing an agent needs to invoke this correctly or to set expectations with a user is missing.

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% for the single username parameter, including an example, so the schema already does the parameter work. The description adds only the framing that the name is both reserved and prefilled, which is useful but not syntax or format detail beyond the schema — baseline 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 artifact: it returns a link that opens Kulhad sign-up with a page name prefilled, to be handed to the person doing setup. It explicitly disambiguates from the sibling check_username_available (and from 'create account', which it says is impossible), so an agent can tell it apart 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?

It gives clear context for use: get the link, hand it to the person setting up the page, who finishes in a browser. It also draws boundaries (does not create an account and cannot; does not block direct signups). It stops short of explicitly naming when to prefer a different tool path, so it is strong context rather than full alternative routing.

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