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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the scoping behavior of the types parameter (short overview vs. specific types vs. all), but does not disclose details like output structure or potential size of the 'all' guide. That is acceptable for a simple read-only tool with annotation coverage, hence a 3.

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 sentences with no filler. The primary action is front-loaded, and the second sentence provides a concrete usage example and an explicit when-not-to-call rule. Every clause earns its place.

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 documentation/helper tool with one optional parameter and no output schema, the description covers the main usage modes (short overview, specific types, full guide) and tells users when the tool is unnecessary. It could be slightly more explicit about what 'details' or 'full guide' returns, but the title and schema fill in enough context, making the definition sufficiently complete.

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 already documents the types parameter thoroughly, including that omitting it returns a short overview, that items are enums, and that ['all'] returns the complete guide. The description restates some of this information and provides examples like 'types:["triangle","connector"]', but adds no substantially new meaning. With 100% schema coverage, the baseline of 3 applies.

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 'Read a short canvas overview or request details for only the needed types', clearly identifying a specific action and resource. The title 'Learn selected canvas JSON' reinforces the educational purpose, and the description distinguishes this from sibling tools by positioning it as a guide rather than a drawing/retrieval mutation operation.

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 explicitly states when to call the tool ('request details for only the needed types', 'Use types:["all"] for the full guide') and when not to call it ('Ordinary rectangle and arrow diagrams can use the input schemas without calling this tool'). This gives clear context and an alternative, satisfying the when/when-not criteria.

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