apply-category

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

The description goes well beyond the annotations (readOnlyHint=false, destructiveHint=false) by detailing exact mutation semantics: `set` replaces, `add` appends, `remove` removes only named categories. It also discloses the matching-by-display-name behavior, the Graph `$batch` mechanism, and the per-message confirmation return, all of which are non-obvious and useful.

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 four sentences long, each earning its place. It starts with the core purpose, then explains actions, parameter options, prerequisites, and return value in a logical flow. No redundant filler or restatement of the tool name.

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 tool with four parameters, no output schema, and moderate complexity, the description covers all necessary aspects: purpose, action semantics, prerequisite (categories must exist), single/batch variants, and return value. It also correctly references the sibling `manage-category` tool, making the description complete in context.

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?

While the input schema already covers all parameters (100% coverage), the description adds critical meaning: it explains that `messageId` and `messageIds` are alternatives (not combinable), that `categories` are matched by display name, and that `action` defaults to `set`. This extra context enriches the parameter understanding beyond the schema's terse 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 opens with a clear verb+resource statement: 'Tag or untag email messages with master categories.' It specifies the three actions (set, add, remove) and distinguishes itself from sibling tool `manage-category` (which creates categories). The purpose is unambiguous and specific.

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 clear context by referencing `manage-category` as the prerequisite for creating categories and explicitly notes that category names must already exist in the master list. It also explains single vs. batch usage. It doesn't explicitly list alternative tools for 'when not to use this', but the workflow context is strong enough to guide selection.

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