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

Annotations already declare non-read-only, idempotent, non-destructive behavior, so the description only needs to add context. It does add which flags are changed, but it omits important behavior such as what happens when seen or flagged is omitted, and whether auth or ownership restrictions apply.

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 description is a single efficient sentence with no wasted words, and it front-loads the core action and affected flags.

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 three-parameter mutation tool with no output schema, the description conveys the core purpose and flag meanings. However, it omits the required message id and the semantics of omitted boolean parameters, which are necessary for fully correct invocation.

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 0%, so the description must carry parameter meaning. It partially explains the seen and flagged booleans through the phrases 'seen or unseen' and 'flagged or unflagged', but it does not mention the required id parameter or clarify omitted-flag behavior, leaving substantial gaps.

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 uses a specific verb ('Marks') and resource ('a message') and names the exact flags affected (seen/unseen, flagged/unflagged). It is clear what the tool does, though it does not explicitly distinguish itself from siblings like mail_move or mail_delete beyond the flag-setting scope.

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?

The description implies the tool is used to change seen or flagged status, but it gives no guidance on when to use it versus alternatives or any preconditions. There are no exclusions or comparisons to sibling tools such as mail_get or mail_list.

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