mail_get_messages

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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower, yet the description adds substantial behavior: the hard 10-reference ceiling, per-reference results returned in input order, sanitized errors instead of failures, and overflow to a private JSON file with a summary and no silent drops. That is exactly the kind of contract an agent cannot infer from annotations or schema.

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?

Four tightly packed sentences, front-loaded with the batch-read contract, then default behavior, then return semantics. No filler. Slightly dense in the back half, but every sentence earns its place.

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?

With no output schema, the description does the heavy lifting by explaining the per-reference result/error shape, input-order guarantee, and file-overflow behavior. The main gap is undocumented previewBytes and addressing fields, which leaves the calling contract slightly incomplete.

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 only partially pays it: it clarifies includeBodies ('request bodies explicitly') and hints at full addressing ('exact message references'), but previewBytes is never explained and the accountId/folder/uid/uidValidity quartet is left entirely to the schema. Baseline 3 for a 3-param tool with no schema text.

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+scope: reads up to 10 exact message references across folders/accounts in one call. The batch framing and 'exact references' wording implicitly separate it from the singleton mail_get_message and from mail_search_messages/mail_list_messages. It stops short of naming a sibling explicitly, which is the only thing keeping it from a 5.

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?

'Metadata and headers only by default; request bodies explicitly' gives real guidance on the includeBodies toggle. However there is no when-to-use-this vs mail_get_message/mail_search_messages/mail_list_messages routing, and no prerequisites (e.g., needing uidValidity from a list call). Usage is implied rather than stated.

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