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

With only readOnlyHint available in annotations, the description carries the rest of the burden and delivers the key behavioral fact an agent needs: authentication is mandatory before this call and a login session triggers it. No return format or pagination detail, but the auth gate is well disclosed.

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?

Front-loaded with the purpose, followed by a compact ACCESS block giving the exact remediation steps. Two functional sentences, no filler; only minor overlap between the authentication instruction and the sign-in alternative.

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 zero-parameter, read-only list tool with no output schema, the only real complexity is the auth requirement, which is fully addressed including the fallback path via start_login. Nothing essential to correct invocation is missing.

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?

The tool takes zero parameters, so the baseline is 4. The description correctly does not invent parameter details and instead spends its text on the auth prerequisite.

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: 'List all email addresses associated with the authenticated account.' This is clear and distinguishable from adjacent list tools like list_phones, though it does not explicitly name siblings to distinguish itself from.

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?

Provides concrete prerequisite context: a Proof account is required, the client must be authenticated, and the alternative path (start_login, then re-call this tool) is spelled out. It stops short of explicit when-not-to-use guidance relative to sibling list/email tools, but the invocation context is unambiguous.

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