set_primary_email

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

Annotations already declare destructiveHint=true and readOnlyHint=false, so the mutation risk is signaled structurally. The description adds genuine value with the authentication/session requirement, but it does not disclose what the destructive change actually entails — whether the previous primary is demoted or dropped, and whether the target address must be verified first.

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 sentences with the core action front-loaded and the access requirement second; no filler. The ACCESS sentence is somewhat dense with two alternative authentication paths, but every clause is actionable.

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?

An output schema exists, so return values need not be explained, and the auth prerequisite is covered. For a destructive account-level mutation, though, the definition leaves out key preconditions and side effects (verification state of the address, fate of the prior primary), which an agent needs before invoking it.

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 'id' is documented as 'Email record ID to set as primary.' The description adds nothing about the identifier format or how to obtain it (e.g., from list_emails), so the baseline 3 applies when the schema carries the parameter semantics.

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?

The description states a specific verb and resource: 'Set an email address as the primary email for the account.' An agent can immediately tell this is a mutation of the primary-email designation. It does not distinguish itself from nearby siblings such as list_emails, start_add_email, or set_primary_phone, so it stops short of a 5.

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 sentence gives a real precondition (a Proof account plus either PROOF_API_KEY or a session via start_login), which is useful when-to-use context. However, it never says when to prefer this over start_add_email or verify_email_otp, nor what state the email must already be in, so the alternative-selection guidance is only implied.

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