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

Annotations declare destructiveHint=true and readOnlyHint=false, and the description explains exactly what is destructive: the previous primary profile is demoted to secondary. It also discloses the authentication prerequisite. That is meaningful context beyond the annotations, though it doesn't cover failure modes or reversibility.

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 core effect is front-loaded in the first sentence and the access requirement follows in a compact block. The CLAUDE-Code-specific parenthetical is slightly verbose but earns its place as actionable remediation.

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 annotations covering the safety profile and no output schema, the description covers the state transition and auth prerequisite adequately. Only minor gaps remain, such as behavior when the target profile is already primary or the ID is invalid.

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% and the single profile_id parameter is already documented in the schema. The description adds no format, sourcing, or resolution guidance for that ID, 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 specific verb (set) and resource (profile as primary) and even describes the resulting state change. It doesn't contrast itself with siblings like set_primary_email or set_primary_phone, but the resource is unambiguous enough that an agent can select it.

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 description gives an important precondition (needs a Proof account; authenticate first; start_login does not cover this) which is genuine usage guidance. However, it never says when to prefer this over alternatives such as update_profile or update_my_profile, so the when-to-use dimension is only implied.

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