mail_needs_response

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

Far exceeds what annotations cover: discloses the heuristic basis (headers + message properties, no body read), the 25-result cap and the meaning of truncated, and the Automation permission requirement. These are exactly the behaviors an agent needs before calling, none of them stated by readOnlyHint/destructiveHint.

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 and reasons, then constraints, then output shape and permissions — well ordered with no filler. It is dense and slightly crammed (reason codes, folder contract, cap, auth in one block), but every sentence carries operational value.

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?

Although an output schema exists, the description still clarifies the important return semantics (truncated = 25 cap reached) and the reason taxonomy. Combined with permission requirements, the fixed folder contract, and the zero-param rationale, an agent has everything needed to call and interpret it.

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?

With zero parameters the baseline is 4, but the description explains the implicit design decisions that a schema cannot: why there is no account argument (unified inbox, owner genuinely unknown) and the fixed folder='inbox' that makes returned ids directly reusable. That is real added meaning, not schema repetition.

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+resource ('Inbox messages that likely need your response') plus the ranking signal (reason codes flagged/unread-direct/unanswered-direct), and explicitly names a sibling (mail_search) it is not. An agent can distinguish this from mail_awaiting_reply or mail_overview without opening the schema.

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 routing rule: use mail_search when the owning account matters, since this tool spans the unified inbox so account is unknown. It also states the ids are directly usable in mail_body/mail_reply, removing a lookup step. It does not, however, contrast with the similarly named mail_awaiting_reply sibling, leaving one ambiguous boundary.

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