mail_setup

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

Despite having annotations, the description adds substantial behavioral context beyond them: it checks local storage before prompting for credentials, reports process identity, rejects known Windows Codex sandbox accounts, accepts no password, and only mutates local account settings when the user submits the form. This is consistent with readOnlyHint=false / destructiveHint=false and materially informs the agent.

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, and subsequent sentences each carry distinct behavioral or safety information (storage check, sandbox rejection, URL handling, no-password, scope of mutation). It is dense and slightly long, but no sentence is filler.

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 no output schema, the description must hint at the return value, and it does ('the returned URL'), plus it covers side effects and constraints thoroughly. Minor gaps remain (URL lifetime, form contents), but 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 reinforces this by stating 'Accepts no mailbox password,' confirming there is nothing to supply at call time.

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 gives a specific verb+resource: 'Start or reuse a private local mailbox login form in the actual MCP process.' The scope qualifier ('in the actual MCP process') and the 'start or reuse' framing make it distinguishable from a status/query tool, but it never names or contrasts with siblings like mail_setup_status or mail_accounts.

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?

It tells the agent what to do with the result ('Open the returned URL in the app browser or give it to the user') and states a clear prohibition ('never read the filled form'), which is genuine operational guidance. It stops short of explicit when-to-use/when-not-vs-alternative routing among the many mail_* siblings.

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