Modify Labels on a Gmail Message

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

The description discloses the return behavior ('Updated message with its current label IDs') and notes that removing the INBOX label archives the message. Annotations already indicate this is a mutating operation (readOnlyHint: false), so the added context is useful and does not contradict any annotation.

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 well-structured with Args, Returns, and Examples sections, making it easy to scan. However, the Args section partially duplicates the schema, adding some redundancy. Overall, it is focused and every sentence carries useful information.

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?

The description is complete for a tool of this complexity: it covers purpose, parameters, return value, and common use cases. With no output schema or explicit prerequisites, the description still gives enough detail for an agent to invoke the tool correctly.

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?

Despite 100% schema description coverage, the description adds significant value by providing common system label IDs (INBOX, STARRED, etc.) and concrete examples for each parameter (e.g., 'Star message abc123' -> add_label_ids: ['STARRED']). This goes beyond the schema's basic parameter descriptions.

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 'Add or remove labels (tags) on a specific Gmail message', which is a specific verb+resource+scope. It distinguishes from sibling tools like gmail_modify_thread_labels (modifies a thread) and gmail_bulk_label_by_search (bulk operation) by emphasizing 'specific Gmail message'.

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 provides concrete usage context with 'Use gmail_list_labels to find label IDs' and multiple 'Use when' examples. It does not explicitly exclude alternatives like thread-level or bulk operations, but the examples make it clear this is for single-message label modifications.

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