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

No annotations are provided, so the description carries the full burden. It discloses a genuinely useful side effect (previous primary becomes secondary) and the authentication prerequisite, which goes beyond the schema. However, it does not disclose mutation reversibility, behavior if the target profile is already primary, or the return value. It adds meaningful context but is not exhaustive.

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 the first sentence with the side effect immediately following. The access note is a separate block that earns its place by preventing a failed call, though it is slightly verbose relative to the tool's simplicity.

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 single-parameter tool with no output schema and no nested objects, the description covers the action, the key side effect, and the access prerequisite. The main gaps (already-primary behavior, response format) are minor for this level of complexity.

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% — profile_id is already documented as 'Profile ID to set as primary'. The description reinforces the primary/secondary semantics but adds no syntax or format detail beyond the schema. At 100% coverage, baseline 3 is appropriate.

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 (Set) and resource (profile as primary), and adds the key behavioral side effect that the previous primary becomes secondary. This distinguishes it from siblings like update_profile, create_profile, set_primary_email, and set_primary_phone.

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 access context: requires a Proof account and explicit authentication via /mcp → Authenticate before the tool works. It also names an exclusion (start_login does NOT open this tool), which helps the agent avoid a wrong path. It doesn't explicitly contrast with siblings like update_my_profile or set_primary_email, but the primary-vs-secondary framing makes the intended use clear.

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