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

Annotations already declare readOnlyHint=false and destructiveHint=false, so the write/non-destructive profile is covered. The description adds genuinely non-obvious behavioral context: the mermaid-only input expectation and the post-creation citation protocol (cite as [[diagram:ID]] on its own line, never as [[board:ID]]). It stops short of stating auth/workspace requirements beyond what the schema already notes.

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?

Roughly four tight sentences, front-loaded with the identity/exclusion before the input format and the post-create citation rule. No filler or repeated annotation data.

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?

No output schema, but the description reveals the artifact's identity (the returned ID) via the citation format, so the agent knows what comes back. With 0 required parameters the tool is tolerant, and schema handles the input format; only a note on auth/workspace defaults is missing.

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 67%; the 'source' parameter carries a rich schema description covering node shapes, link syntax, subgraphs and styling, and 'workspace' documents token behavior. The description only says 'Pass the mermaid source', adding a pointer rather than new semantics, and 'title' stays undocumented in both places. Baseline 3 for a schema doing most of the work.

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, then pins down the artifact type ('interactive FLOWCHART — process, decision tree, system map') and explicitly names the two siblings it is not (napkin_docs_create, napkin_boards_create). An agent can distinguish it from every other napkin_* create tool without opening a 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?

Gives a positive trigger ('Use for process maps the user asked you to draw') and explicit exclusions routed to alternatives by name. Nothing about when to pick this over the doc/board create tools is left to inference.

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