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

Annotations already flag destructiveHint=true, so the description does not need to restate that. It adds useful context about being translucent, behind nodes, and not reparenting, but it does not disclose what happens to existing regions, whether this is reversible, or what the destructive aspect actually includes. Overall it adds some transparency beyond annotations but leaves gaps.

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 tight paragraphs with no filler. The first sentence explains purpose, the next gives clear when-to-use, and the final line scopes it to one diagram. Every sentence contributes value.

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?

Without an output schema, the description covers the main usage: what it does, when to use it, prerequisites, and sizing guidance. It does not explain return values or what happens to pre-existing regions, but those are partly covered by annotations and schema constraints. Overall it is complete enough for an agent to invoke 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?

The schema covers 50% of top-level parameters and documents nested fields like color and label. The description adds meaningful guidance: 'size the region to enclose the nodes with roughly 24px of margin' gives operational meaning to width/height and coordinates. It also clarifies diagram_id refers to one Datadef diagram. It does not enter coordinate/units detail, but it compensates well for the schema coverage.

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 a specific verb and resource: 'Draw a labelled translucent area behind existing nodes to show they belong together, without reparenting them.' It immediately distinguishes the tool from canvas_group_nodes, which moves nodes into the zone. The title 'add region' is expanded with concrete behavior.

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?

Explicit usage guidance is provided: 'Use this when the grouping is a reading aid rather than real containment, when areas would need to overlap, or when a node belongs to two ideas at once.' It names the alternative canvas_group_nodes and explains why it fails. It also recommends calling canvas_measure_canvas first and provides a margin size.

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