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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuinely new context beyond that: an authentication requirement ('Needs a token') and the default page size of 20, which affects result volume. It stops short of describing return fields or how to request further pages, keeping it out of the top band.

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 and the middle sentences form a tight call-ordering chain. The trailing 'Needs a token. Optional limit (default 20).' partly duplicates schema content, which is the only minor waste.

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 simple read-only list tool with no output schema, the description covers purpose, auth prerequisite, default result count, and next-step tools. Return field shape is unspecified, but the complexity is low enough that this is a small gap rather than a blocking one.

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 description coverage is 100% and all three parameters are already documented in the schema, including the email format and the limit default. The description only restates the token requirement and the limit default, adding no syntax or format nuance beyond the structured data, so the baseline 3 applies.

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 received emails for its @divindi.io address.' It also explicitly contrasts with divimail_sent for outgoing mail, so the agent can distinguish it from siblings without consulting schemas.

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 an explicit workflow: 'Call this first to see what arrived, then use divimail_read with a messageId ... and divimail_mark_read when done,' plus a named alternative (divimail_sent) for the opposite use case. This is textbook when-to-use and when-not guidance.

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