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

Annotations already state readOnly=false, idempotent=false, and destructive=false. The description adds valuable behavioral context beyond that: IMAP IDs encode folder+UID, change on moves/draft updates, and must always come from the last operation. No contradiction with annotations.

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 core purpose is front-loaded, but the description becomes a dense run-on that repeats the schema text nearly verbatim and lacks clear structure, e.g. 'after a change Never pass'. Bulleted caveats would make it much easier to scan.

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 mutation, the description covers the critical resolution workflow, ID acquisition, IMAP ID-staleness, and forbidden input values. Account_id handling is covered in the schema. The only minor gap is no mention of the return shape since there is no output schema.

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%, so a baseline of 3 applies. The description adds extra meaning with 'Resolve human email reference -> email_id first' and reinforces what must never be passed, which helps the agent construct the email_id parameter correctly.

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 opens with 'Mark one exact email read', a specific verb, resource, and scope. The word 'exact' plus the read state distinguishes it from siblings like email_mark_unread and email_read_message without needing to name them.

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 gives a clear workflow: resolve human references to email_id first, obtain IDs from email_list_messages or email_list_folder_messages, and avoid stale IDs on IMAP. It does not explicitly name alternative tools for other read-related intents, so it falls short of a 5.

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