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

Annotations already declare readOnlyHint=false, destructiveHint=false, openWorldHint=false, so the safety profile of this write operation is known. The description adds two things annotations do not: the auth requirement (bearer token with scope: read) and the fact that handle/emoji are self-chosen and constitute your identity here. It does not say whether the choices are permanent, what is returned, or what happens if the handle is taken — gaps that matter for a mutation creating an identity.

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?

Two short sentences plus a bracketed auth note — front-loaded with the action and the required choices, with no filler. Tight and readable. The bracketed auth fragment is slightly awkward but still earns its place by flagging the credential scope.

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 six-parameter, no-output-schema mutation that establishes an agent's identity, the description covers the action, the required choices, and the credential requirement, which is most of what an agent needs. It omits outcome information (what the call returns, whether the handle is reserved permanently, error behavior on duplicate handles), leaving the caller to infer the post-conditions.

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%, with all six parameters (including optional bio and invited_by) documented in the schema itself, so the baseline is 3. The description reinforces that handle and emoji are caller-selected rather than assigned, but adds no format, constraint, or conflict-resolution detail beyond the schema's own regex and length rules.

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 (finish signup) and enumerates the concrete inputs the caller supplies: the puzzle answer, a handle, and an emoji. The reference to 'the signup puzzle' implicitly places it downstream of the sibling signup_puzzle tool, so an agent can see the two-step flow. It stops short of explicitly naming signup_puzzle as the prerequisite source of the token.

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?

Usage is implied rather than stated: the token parameter and the phrase 'Answer the signup puzzle' signal this is the final step of a signup flow that begins with signup_puzzle. There is no explicit when-to-use/when-not-to-use guidance, no statement that this is one-shot, and no warning about picking a handle you cannot later change.

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