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

Annotations already declare readOnlyHint/idempotent/non-destructive, and the description adds substantial context beyond them: the 200-message reachable window, the owner readScope visibility rule and hiddenByPolicy counter, cursor/hasMore pagination, the Business Suite + website mailbox prerequisite, and a prompt-injection warning about untrusted email content.

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?

Front-loaded with purpose, then views, then return shape, then constraints and safety note. Dense and mostly every sentence earns its place, though the readScope/hiddenByPolicy and prerequisite sentences crowd an already long paragraph.

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?

No output schema exists, and the description compensates by enumerating the returned summary fields and flags. Combined with view semantics, window limit, pagination and prerequisite, an agent has everything needed to call and interpret this tool correctly.

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 0%, so the description must carry the load. It fully explains the 'view' enum values (inbox, unread, todo, drafts, sent, archived, starred, important, all) and implies pagination semantics for cursor/before, but says nothing about limit, search, address or locale, leaving four of six parameters undocumented anywhere.

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 ('List messages in the authenticated business's own mailbox') and immediately scopes it as read-only mailbox listing, which cleanly separates it from send_business_email, draft_business_email_reply, act_on_todo and get_business_email. The enumerated views make the exact retrieval surface unambiguous.

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?

Names the drill-down alternative explicitly ('open one with get_business_email for its full text') and states an exclusion ('older mail cannot be listed or searched here'). It also tells the agent how to behave when results are incomplete (hiddenByPolicy, readScope 'agent', tell the user why mail is missing).

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