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

Beyond the annotations (destructiveHint=true, openWorldHint=false), it discloses that the diagram is modified and regenerated, that the id must come from an actual prior response, and that each call costs 15 coins — real budget and provenance context the annotations do not carry. It does not say whether prior content is irrecoverably replaced or whether a new diagram id is issued.

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?

Four short sentences, front-loaded with what the tool does and followed by the prerequisite and cost. 'Modifies the diagram based on your instructions and regenerates' partially restates the opening sentence, a small redundancy in an otherwise tight block.

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 two-param, non-nested tool with a fully documented schema and annotations covering safety, the description supplies the prerequisite, cost, and mutation model. The one gap is return behavior — with no output schema, an agent cannot tell whether a new diagram_id or artifact is returned for follow-up calls.

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%, so both parameters are already fully documented, including the provenance constraint on diagram_id and the natural-language character of instructions. The description restates the diagram_id requirement rather than adding syntax, length limits, or example semantics beyond the schema's own example.

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 ('Edit') plus resource ('existing Excalidraw diagram') and the mechanism ('natural language instructions'), which cleanly separates it from create_excalidraw and the other edit_* siblings. The pointer back to create_excalidraw as the source of diagram_id reinforces the workflow position.

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?

Makes the precondition explicit ('Requires diagram_id from a previous create_excalidraw response') and indicates the mutation cost, which tells an agent when this call is warranted versus creating anew. It stops short of naming a when-not-to-use case or an alternative editing path, but none exists among the siblings.

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