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

The annotations only indicate non-readonly and non-destructive, which is consistent with the description's 'creates' language. The description adds meaningful behavioral context beyond the annotations: the room_id behavior, arrow auto-binding within 30px, rich-text HTML subset, and color handling. This goes well beyond the minimal hints, though it doesn't cover every edge case.

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 fairly long but well-structured with clear section headers (Rich text, TEXT IN SHAPES, ARROWS, Colors). The main purpose is front-loaded. Some redundancy exists with the schema (e.g., the HTML subset is repeated), but each section provides useful guidance. Overall, it earns its length without being bloated.

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 complexity (multiple element types, rich text, arrow binding, canvas creation), the description covers key aspects well: usage context, element types, rich-text constraints, arrow positioning, and color format. An output schema exists, so return values are not needed. Minor gaps include lack of coordinate system explanation and the textAlign reference without a schema parameter, but the description is still highly complete for a complex tool.

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 coverage is 100%, so baseline is 3. The description enriches this by explaining when room_id should be used, elaborating on the element types and their inferred defaults, explaining containerId for bound text, and detailing arrow binding behavior. It adds value over the schema descriptions, though some details (like textAlign) are mentioned in the description but not present as a schema property.

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 tool creates elements on a canvas and distinguishes between creating a new canvas or adding to an existing one via room_id. It explicitly names the sibling tool add_elements_from_mermaid and explains when to use that instead, making the purpose and scope unambiguous.

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 explicit 'when to use' guidance with concrete use cases (wireframes, UI mockups, freeform illustrations, etc.) and directly says 'For diagrams Mermaid can express, use add_elements_from_mermaid instead.' It also explains when to pass room_id versus omit it, giving clear alternatives.

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