Apply a label in bulk

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

The description adds the useful behavioral note that 'Messages stay where they are,' which is not captured by annotations. It also states 'one existing label,' implying the label must pre-exist. However, it does not explain behavior on invalid uids, missing labels, or return values. Given that annotations already cover readOnly/idempotent/destructive hints, the description contributes some but not rich additional context.

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 two short sentences, front-loaded with the main action and a clarifying note about message placement. Every word earns its place; no unnecessary detail or repetition.

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?

Given the tool's moderate complexity (5 parameters, no output schema), the description, combined with rich schema descriptions and safety annotations, is largely complete. It clarifies the core behavior (no move) and relies on the schema for parameter details. The only gap is the absence of any mention of return/result behavior, but that is not critical for a bulk action with no output schema.

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?

The input schema has 100% coverage with detailed descriptions for all parameters (uids, label, folder, dry_run, uidvalidity). The description adds no extra parameter semantics beyond what the schema already provides, so the baseline of 3 is appropriate.

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 states exactly what the tool does: 'Apply one existing label to many messages.' It is specific (apply label, bulk scope) and differentiates from sibling tools like bulk_move by noting 'Messages stay where they are.' This clearly distinguishes it from move operations and from single-label tools like apply_label.

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 gives clear context: it is for bulk application of an existing label. However, it does not explicitly say when to use this tool versus alternatives (e.g., apply_label for single messages or bulk_move when moving is desired). The phrase 'Messages stay where they are' implies it is not a move, but there is no direct guidance or exclusion.

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