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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the description is free to spend its words on the return contract, which it does: ok/errors/warnings plus code, offending element, and one-line fix. It does not state what happens if neither or both inputs are supplied (both are optional), which is the one behavioral hole.

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?

Two sentences, zero filler, and the single most decision-relevant fact ("without saving it") is placed up front. The second sentence delivers the return shape compactly in one clause chain.

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?

Because there is no output schema, the description correctly spends its second sentence explaining return values, and the nested scene object is delegated to an external schema URL in the input schema. The gap is that neither parameter is required, and the description doesn't say whether exactly one input must be provided or how the two are combined.

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% and the mermaid property already carries the erDiagram/flowchart limitation note, so the schema does the heavy lifting. The description only names the two input kinds ("DSP scene or Mermaid text"), adding no format or size detail beyond the structured fields; baseline 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?

States a specific verb ("checks") over a specific resource ("DSP scene or Mermaid text") and adds the scoping qualifier "without saving it," which separates it from diagram_create and diagram_edit. An agent can pick it out of the diagram_* family without opening the schema.

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 phrase "without saving it" implies a pre-save validation workflow, which is useful context, but the description never names an alternative or an explicit when-not-to-use condition. There is no guidance on using this before diagram_create versus after diagram_edit, so usage is only implied.

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