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

Annotations already declare readOnly/openWorld=false/destructive=false, so the safety profile is covered. The description adds genuinely new behavioral facts: the Pro entitlement requirement, the account scoping, newest-id-first ordering, and the Message-ID staleness caveat. No pagination/limit behavior is disclosed, which keeps it short of a 5.

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?

Dense and front-loaded: purpose, ordering, returned field, filters, sequencing constraint, category semantics, entitlement. Every sentence earns its place, though it packs many clauses into one paragraph rather than separating the sequencing advice.

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 needn't be enumerated, and the description still flags the one field that matters (Message-ID). It covers scope, filters, ordering, entitlement, and the update_draft dependency. The only real gap is limit/pagination behavior for a list that can default to 50 items.

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 carries the burden — and it does: match_subject / match_to / match_account are described as case-insensitive substrings, and category is described with an example ('Work'). Only 'limit' is left undocumented, so the compensation is strong but not complete.

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?

Starts with a specific verb and resource ('List drafts'), then bounds scope ('accounts this server is scoped to') and ordering ('newest id first'). It also states what each row carries ('current Message-ID for update_draft'), which tells an agent why this tool exists rather than just what it is.

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?

Explicit when-to-use: 'Call this immediately before update_draft' with the reason (Message-ID changes on Mail re-sync). It also names the three narrowing filters and what 'category' selects, so the agent knows how to route to this tool versus show_draft or search_mail.

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