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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered by structured data. The description's added value is the return content (ids, addresses, folders) and the id-to-accountId linkage, which is useful but modest; it says nothing about ordering, volume, or whether accounts are cached.

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 short sentences, each doing distinct work: the first defines the resource and its returned fields, the second explains how to use the result. Nothing is repeated from the title or annotations and the key chaining hint is front-loaded.

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, closed-world listing tool with no output schema, the description supplies the missing return-value information (ids, addresses, folders) and the id usage contract. An agent has everything needed to call it and act on the result.

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 schema has zero parameters, so there is no parameter semantics for the description to explain and the baseline of 4 applies. The description correctly spends its words on return shape and id reuse instead of inventing parameter detail.

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 ('Lists all GhosterMail mailboxes') and immediately disambiguates the domain term by glossing mailbox as 'e-mail account', so an agent knows exactly what comes back. It does not explicitly contrast itself with create_accounts or delete_accounts, but the read-only 'list' framing makes the split obvious.

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 concrete downstream guidance: 'Use the returned id as accountId in other tools', which tells the agent this is the discovery step preceding list_messages, read_message, send_message, etc. It stops short of naming a specific sibling or stating when not to call it (e.g., no pagination or filtering caveats), so it is clear context rather than full when/when-not routing.

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