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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the bar is lower. The description still adds real context: the listing is permission-scoped ('allowed to see'), the result includes the configured scope, and accounts carry categorical labels that affect downstream filtering. It stops short of stating return shape or pagination, which keeps it out of 5 territory.

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?

Purpose and the 'call this first' directive are front-loaded, which is exactly right. Five short sentences is a bit long for a zero-argument list tool, and the categories/labelling sentences partially overlap with the output schema, but nothing is genuinely wasteful.

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 spelled out. Combined, the description covers what the tool does, when to call it in the workflow, how to pick between account labels, and where to go if the categorization is unclear — everything needed to invoke it correctly.

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 per the baseline rule this lands at 4. The description adds no parameter detail because there is none to add.

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 the Apple Mail accounts') and immediately scopes it as permission-bounded ('this server is allowed to see'). It is clearly distinguishable from search_mail, show_mail, and list_categories without opening any schema.

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?

Explicitly tells the agent to 'Call this first' before filtering a search by account, which is a clear ordering constraint. It also routes to a sibling ('call list_categories if unsure') and gives a decision rule for Personal vs Work accounts.

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