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

Annotations already declare readOnlyHint=false and destructiveHint=true, and the description adds meaningful scope: only the addressed cells are modified, which tells the agent the blast radius of a 'destructive' call. It does not describe the response or the needs_confirmation/approvalId flow, but that flow is documented in the schema.

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?

Three sentences, front-loaded with the core action and address format, followed by scoping behavior and workflow guidance. Every sentence earns its place with no filler.

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 5-param write tool with no output schema, the description covers the action, addressing, blast radius, and prerequisite lookup. The main gap is the return shape (e.g., which cells were written), though annotations already carry the safety profile.

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 description coverage is 100%: cells, sheetId, tabName, workspace, and approvalId are all documented in the schema, including the A1→value map, default tab behavior, and approval flow. The description reiterates the A1/formula format and adds a header-row convention, but the schema already carries the parameter burden, so 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 and resource ('Sets cells in one tab of a sheet'), names the addressing scheme (A1), and the accepted value types (raw values or formulas with an example). The 'additive and surgical: only the addressed cells change' line distinguishes it from bulk write siblings like napkin_sheets_update and napkin_sheets_create.

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 concrete when-to-use context: call napkin_sheets_schema first to learn tab names and where data ends, put headers in row 1 for a new region, and use one call for a whole small table. It does not explicitly contrast with the sibling napkin_sheets_update, so routing between the two write tools still requires inference.

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