gmail_preview_message

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

Adds context beyond the annotations: it mirrors the send path exactly so validation is faithful, and it reports the detected content_type. The read-only guarantee is restated but reinforces the readOnlyHint. It does not say how validation failures are surfaced or whether attachments/paths are checked for existence.

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?

Three short sentences, front-loaded with the core dry-run behavior, with the sibling reference and the return hint following. No filler.

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?

There is no output schema, and the description only partially covers returns (the rendered message and content_type) without describing validation error reporting or structure. For a 9-parameter preview tool, that leaves a meaningful gap.

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 9 parameters and only 33% schema description coverage, the description must compensate but does not: to, subject, body, cc, bcc, thread_id and attachment/inline-image semantics are never explained beyond the schema's own text. The only param-adjacent content is the content_type detection, which loosely maps to is_html.

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 (validates/previews) and resource (the exact message gmail_send_message_strict would send), and explicitly contrasts with the sibling send tool. The agent can distinguish dry-run from actual send without opening either 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?

Clear implied usage: call this to check a composition before invoking gmail_send_message_strict, with the sibling named. No explicit exclusions or edge conditions (e.g. whether it should be used for every send or only HTML/complex bodies) are given.

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