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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the mutation/safety profile is covered. The description adds genuinely useful behavior context beyond that: the auth requirement and the /mcp or start_login flow. It omits what happens if the username is already taken, which is the main remaining gap.

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?

Purpose is front-loaded in the first sentence, constraints follow, then access notes. Efficient overall, though the length/character constraints duplicate what the schema already states, which is mildly wasteful.

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 mutation with no output schema and annotations covering the safety profile, this covers purpose, constraints, and auth. Only minor omissions remain, such as conflict/failure behavior when a username is unavailable.

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% and the single parameter fully documents pattern, min/max length. The description's '3-30 characters, alphanumeric and underscores' repeats the schema verbatim rather than adding new meaning, so the 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?

States a precise verb+resource ('Claim a unique username') scoped to the authenticated user's public profile. No sibling tool in the list does anything similar, so an agent can identify it immediately without opening the 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?

Gives clear prerequisite context: needs a Proof account, and either authenticate the client or sign in via start_login, then re-call this tool. This explains the preconditions for use well, but doesn't explicitly contrast with alternatives (e.g., update_profile's username handling).

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