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

Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds scoping (only its own @divindi.io address) and the default limit of 20, but says nothing about ordering, pagination beyond the limit, or whether messages are ever truncated. Adequate but thin beyond what structured fields give.

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?

Four short front-loaded sentences with no filler; purpose, use cases, alternative and prerequisites each appear once. Slight redundancy in restating the limit default already present in the schema keeps it from a 5.

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 small read-only list tool with no output schema, this covers what it returns (sent messages), whose mailbox (the agent's own address), the auth prerequisite, and the sibling to use for the other direction. Return shape and ordering are the only real omissions.

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%, so the schema already documents email, limit and token fully. The description's 'Optional limit (default 20)' simply repeats the schema field description, adding no new meaning such as max values or ordering 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?

States a specific verb and resource ('lists sent messages for its @divindi.io address') and immediately disambiguates from the closest sibling: 'For received mail use divimail_inbox.' An agent can pick this over divimail_inbox or divimail_send without reading 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?

Gives two concrete use cases ('confirm a divimail_send went out' or 'review history') and names the alternative tool for the opposite direction. Missing only an explicit exclusion such as when limit should be raised or when this is pointless to call.

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