updateGoogleSheetIfUnchanged
Write cell values only if the guarded area has not changed since you read it, and get back what was overwritten so the change can be undone. Call once with dryRun:true to obtain the fingerprint, then again passing it as expectedFingerprint. IMPORTANT: this is optimistic and NOT atomic. The Sheets...
This record as markdown: /tools/ark7-google-drive-mcp/updategooglesheetifunchanged.md
What updateGoogleSheetIfUnchanged does on Google Drive
AI agents use updateGoogleSheetIfUnchanged to create or update resources in Google Drive, usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Google Drive environment.
| Parameter | Type | Required | Description |
|---|---|---|---|
dryRun | boolean | — | Write nothing; return the current fingerprint, the guarded contents and what would be written. This is how the first fingerprint is obtained. |
account | string | — | Alias of the Google account to target. Optional — defaults to the session/global default account, or the sole authenticated account. Run manage_accounts list to |
updates | array | Yes | Ranges to write, ValueRange-shaped, same as batchUpdateGoogleSheetValues. Each one must name a bounded rectangle - a single cell, or both corners given as in "S |
maxBytes | number | — | Byte budget for the same (default 131072) |
maxCells | number | — | Budget for the guarded contents returned on a dryRun or a refusal (default 2000) |
guardRanges | array | — | Ranges whose contents must be unchanged. Defaults to the ranges in updates. They need NOT cover the writes - guarding a source block while writing a summary els |
spreadsheetId | string | Yes | Spreadsheet ID |
valueInputOption | string | — | USER_ENTERED (default) parses formulas; RAW stores them as text. SECURITY: USER_ENTERED evaluates formulas, so never use it with untrusted input. |
expectedFingerprint | string | — | The fingerprint returned by a previous dryRun call. Required unless dryRun is true. |
Parameters from the server's own tool schema.
Why updateGoogleSheetIfUnchanged is rated Medium
An AI agent can call updateGoogleSheetIfUnchanged faster than any human can review: one bad instruction and it creates or modifies resources in Google Drive by the hundred, each call as confident as the last.
Risk signalsHigh parameter count (11 properties)
Attacks that exploit this kind of access
The rule that runs updateGoogleSheetIfUnchanged safely
PolicyLayer is an MCP gateway: it sits between your AI agents and Google Drive, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For updateGoogleSheetIfUnchanged, this is the rule to start with:
updateGoogleSheetIfUnchanged stays usable, but capped: an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
The button opens the PolicyLayer dashboard: create your workspace, connect Google Drive, apply this rule, and every updateGoogleSheetIfUnchanged call is checked against it from then on.
Questions about updateGoogleSheetIfUnchanged
Write cell values only if the guarded area has not changed since you read it, and get back what was overwritten so the change can be undone. Call once with dryRun:true to obtain the fingerprint, then again passing it as expectedFingerprint. IMPORTANT: this is optimistic and NOT atomic. The Sheets API has no compare-and-swap - unlike Docs, where ifRevisionId is enforced by the API itself - so the check happens in this server, and a write landing in the gap between the read and the write (well under a second) is not caught. It catches the case that actually happens: the model changed since you last looked. To undo a write, call again with updates set to the returned preImage and expectedFingerprint set to the returned postFingerprint - nothing else, since guardRanges defaults to the ranges in updates and preImage already carries exactly the ranges that were written. Any cell listed in the returned hazards cannot be restored by feeding preImage back: updates carries strings, so re-writing the string re-interprets it as a formula, a number or a boolean and the cell changes type. Its native userEnteredValue is returned so that you can restore that one cell outside this server - through the Sheets API's own updateCells, or by hand - so an undo that touches a hazard cell needs that cell handled separately. The hazard list is deliberately not exhaustive: text kept as text via a leading apostrophe is only flagged when it reads as a formula, a number, or TRUE/FALSE - date-shaped text (e.g. '2024-01-01') is not detected. It is categorised as a Write tool in the Google Drive MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
updateGoogleSheetIfUnchanged accepts 9 parameters: dryRun, account, updates, maxBytes, maxCells, guardRanges, spreadsheetId, valueInputOption, expectedFingerprint. Required: updates, spreadsheetId. The full parameter table on this page comes from the server's own tool schema.
Register the Google Drive MCP server in PolicyLayer and add a rule for updateGoogleSheetIfUnchanged: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Google Drive. Nothing to install.
updateGoogleSheetIfUnchanged is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the updateGoogleSheetIfUnchanged rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for updateGoogleSheetIfUnchanged. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
updateGoogleSheetIfUnchanged is provided by the Google Drive MCP server (@ark7/google-drive-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
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