Gmail: Add label

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

Annotations already declare readOnlyHint=false, idempotentHint=false and destructiveHint=true, so the write/safety profile is covered structurally. The description adds context that labels may be system labels (STARRED, IMPORTANT) or user label ids from list_labels, but says nothing about permissions, error behavior, or the fact that this mutates the message.

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?

One compact sentence with the action front-loaded and no filler. The '[UNIFIED]' tag is noise that does not help an agent act, keeping it from a 5.

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 three-required-parameter mutation tool with no output schema and no annotations for auth, the definition covers the label concept well but leaves the required 'site' argument and post-call effects undocumented. An agent could still call it, but would be guessing on one required field.

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% for three required parameters, and the description only implicitly covers message_id and label_ids (with examples and the list_labels pointer). The required 'site' parameter is never mentioned anywhere, leaving a third of the required input unexplained.

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 ('Add one or more labels to a message') and gives concrete examples of label values, which separates it from gmail_remove_label by implication. It never explicitly names the inverse operation, so it stops short of 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?

The description points to list_labels as the way to obtain a user label id, which is a useful discovery hint for the label_ids array. It gives no guidance on when not to use it, required scopes, or whether it can be batched across messages.

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