applyGmailMessageLabels

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

No annotations are provided, so the description carries the full burden. It correctly conveys that the tool mutates labels, but does not disclose details such as idempotency, required permissions, behavior with invalid label IDs, or consequences of calling with no add/remove arrays. The description adds some context about applicable message types but lacks deeper behavioral warnings.

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?

The description is only two sentences, front-loaded with the primary action, and contains no redundant information. Every word adds value, making it appropriately concise.

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?

For a straightforward mutation tool with low complexity, the description provides enough context: the action, the resource, and the types of messages it applies to. However, with no output schema and no annotations, it could be more complete by mentioning return values or edge cases (e.g., empty arrays), but given the simplicity, a small gap is acceptable.

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 100%, so the schema already documents all three parameters (messageId, addLabelIds, removeLabelIds). The description adds no additional parameter-level meaning beyond the generic term 'labels', so it does not exceed the baseline expected when schema coverage is high.

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?

The description clearly states the verb and resource: 'Adds or removes labels from a Gmail message.' It distinguishes this from sibling Gmail tools like listGmailLabels (listing only) and sendGmailEmail (sending) by focusing specifically on label modification.

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?

Provides clear context on when to use it: 'This can be used to label drafts, sent emails, or any existing message in the user's Gmail account.' It does not explicitly exclude alternatives, but sibling tools like listGmailLabels or sendGmailEmail are clearly different operations, so the context is sufficient.

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