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

The description is consistent with readOnlyHint=true and adds context the annotations cannot express: an authentication prerequisite and the fact that start_login is not a path to satisfying it. It does not cover error behavior for unknown external IDs, but the auth disclosure alone lifts it above baseline.

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 purpose is front-loaded in one clear sentence, and the access caveat follows immediately. The ACCESS block is slightly verbose for two facts but each sentence carries actionable information.

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 an output schema present, return values need no explanation, and the auth requirement is covered. The only shortfall is the absence of guidance on resolving the external user ID or handling a not-found case.

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% for the single required parameter, so the schema already documents external_user_id fully. The description only restates that the lookup is keyed by external user ID, adding no format or sourcing detail beyond the schema.

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 and resource ('Get a single verified user and their verifications') and names the lookup key ('by external user ID'), which distinguishes it from list_verified_users and get_verification. An agent can select it 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?

The ACCESS block gives a real precondition (a Proof account and an authenticated client, with an explicit note that start_login does not enable this tool), which is genuinely useful routing. However, it never says when to prefer this over siblings like get_verification, list_verified_users, or get_current_user.

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