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

Annotations establish destructiveHint=true and readOnlyHint=false, but the description goes much further: it discloses that values are stored EXACTLY AS GIVEN by default, that '=B1+B2' becomes literal text unless USER_ENTERED is used, that an error 'Unable to parse range' occurs for unknown tabs, and that the result carries formula_notice. These are non-obvious behavioral details that materially affect invocation and interpretation.

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?

Every sentence earns its place: purpose, a key prerequisite with an example, failure mode with a routing instruction, the important exact-storage caveat with the fix, and a note about the result payload. The most critical constraints are front-loaded, and there is no filler or repetition of schema content.

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 destructive write operation, the description covers the core prerequisites, the error path, the behavioral nuance around formulas, the alternative for creating tabs, and the formula_notice in the result. An output schema exists, so return-value documentation is not the description's burden. Nothing essential is missing for correct tool selection and invocation.

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 the baseline is 3, but the description adds meaningful context beyond the schema: it gives a concrete tab-name example for range, explicitly connects the range requirement to the add_sheet_tab sibling, and reinforces the formula-storage distinction. This elevates the parameter documentation beyond what the schema alone provides, though not to a 5 given the schema is already thorough.

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 a specific verb and resource: 'Write data to a range in an existing Google Sheet.' It clearly distinguishes this from siblings like update_document and update_presentation by targeting spreadsheets, and it implies the sheet must already exist, which differentiates it from create_spreadsheet. The purpose is immediately understandable and unambiguous.

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 gives explicit when-to-use guidance: it states the sheet must already exist, names the failure mode for unknown tabs, and directly instructs the agent to 'call add_sheet_tab first' when creating new tabs. It also tells when to choose value_input_option='USER_ENTERED' instead of the default RAW behavior. This is exemplary routing guidance.

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