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

Annotations already declare readOnly/idempotent/non-destructive, so safety is covered; the description adds non-obvious context beyond them — account-level availability for own projects and the requirement of a per-action spend approval before paid execution. It does not describe output shape, but no output schema exists so that is a modest gap.

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?

Front-loaded with the invocation trigger, then the layout grid rule, then billing constraints — a sensible order. The inline grid math (ceil(sqrt(N)), 16=4x4, 20=5x4) is arguably detail that the returned layout guide would supply, making it slightly heavier than necessary for a discovery call.

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 no-param, read-only documentation tool with no output schema, the description is complete enough: it says what the call returns, when to make it, and the billing constraint that governs subsequent paid actions. Only the relationship to sibling capability/knowledge tools is left unstated.

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?

Zero-parameter tool, so the baseline is 4; there are no argument semantics to explain. The description correctly conveys that it takes no input and simply returns schema/capability/layout documentation.

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?

States a specific verb and resource set: read the Canvas agent operation schema, capabilities and layout guide. An agent can tell it is a pre-flight discovery tool rather than a mutation tool. It does not, however, differentiate itself from adjacent discovery siblings such as aimixer_canvas_continuity_capabilities or aimixer_canvas_knowledge.

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?

Gives an explicit trigger ('when the user asks to create, open, edit or lay out a Canvas, moodboard or storyboard') and an explicit ordering instruction ('call this first'). No exclusions or named alternatives are given, so an agent cannot distinguish this from the other capabilities/knowledge tools by guidance alone.

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