# Query a large Google Sheet from an n8n AI agent

> Give an n8n AI Agent a tool that filters and aggregates a Google Sheet server-side, instead of loading every row into the workflow.

Source: https://datatomcp.com/guides/n8n-google-sheets-ai-agent · By Killian · Updated 2026-10-27

The usual n8n pattern for "let the AI Agent look things up in a sheet" is a Google Sheets node that returns every row, sometimes a Code node to filter, and then the whole result handed to the model. On a big sheet that's slow, it eats tokens, and the agent often only sees the first items.

A better pattern is to give the agent a **tool that queries the sheet server-side**: it sends a filter or a group-by and gets back only the answer. This guide does that with datatomcp and n8n's HTTP Request Tool.

## HTTP Request Tool or MCP Client Tool?

n8n has two ways to give an AI Agent an outside tool:

| | HTTP Request Tool | MCP Client Tool |
|---|---|---|
| Talks to | Any REST API | An MCP server (HTTP Streamable or SSE) |
| Auth options | Any n8n credential (header, bearer, OAuth2) | Bearer, header, multiple headers, MCP OAuth2 |
| The agent sees | One tool you describe | Every tool the server lists, with their schemas |
| Best for | Servers with an API key; full control of the request | OAuth MCP servers that accept n8n's callback |

datatomcp offers both a REST API (API keys) and an MCP server (OAuth sign-in, built for chat and coding agents like Claude, ChatGPT and Cursor). For n8n we recommend the REST API: an API key doesn't expire, needs no browser sign-in on the n8n server, and you can see exactly what the agent sends. The MCP route is the one to use in chat apps; see [how to add a remote MCP server to any AI client](/guides/add-remote-mcp-server).

## 1. Make the sheet queryable

1. Sign in at [app.datatomcp.com](https://app.datatomcp.com/login), **Add data → Google Sheet**, and pick the sheet. Private sheets work: you grant access to that file only.
2. Note the dataset id (`ds_…`) on the dataset page and the column ids in the columns table.
3. Under **Account → API keys**, create a key named `n8n`.

## 2. Add the tool to your AI Agent

1. In your workflow, add an **HTTP Request Tool** to the AI Agent node's tools.
2. Method `POST`, URL `https://app.datatomcp.com/v1/datasets/ds_YOUR_ID/query`.
3. Authentication: a header credential with name `Authorization` and value `Bearer dtm_…`.
4. Send a JSON body and let the model fill it in. Describe the tool so the agent knows the format, for example:

> Queries the sales sheet. Body is JSON: `where` (list of `{column, op, value}`; ops eq, neq, gt, gte, lt, lte, in, contains, between), optional `group_by` (column ids), `metrics` (list of `{fn: count|sum|avg|min|max|count_distinct, column, as}`), `order_by`, `limit`. Columns: order_date (date), country (text), product (text), total (number).

## 3. Try it

Ask the agent:

> Which three products sold the most in Germany in September?

It sends:

```json
{
  "where": [
    { "column": "country", "op": "eq", "value": "Germany" },
    { "column": "order_date", "op": "between", "value": ["2026-09-01", "2026-09-30"] }
  ],
  "group_by": ["product"],
  "metrics": [{ "fn": "sum", "column": "total", "as": "revenue" }],
  "order_by": [{ "column": "revenue", "dir": "desc" }],
  "limit": 3
}
```

and receives three rows, however large the sheet is.

## Tips

- Add a second HTTP Request Tool for `GET /v1/datasets/ds_YOUR_ID/values/{column}` so the agent can look up exact category names before filtering.
- Errors come back as JSON with a readable `message` (for example an unknown column id), which the agent can use to correct its next call.
- The sheet stays current with **Refresh now** in the app, a `POST /v1/datasets/:id/refresh` step in your workflow, or hourly sync on Pro.

## Without the AI Agent

The same HTTP Request (non-tool) node works in ordinary workflows: one node that returns filtered rows or totals, instead of read-all-then-filter. See [Google Sheets as an API](/guides/google-sheets-as-api). The same request works from [Make](/guides/make-query-google-sheet) and [Zapier](/guides/zapier-query-google-sheet).