spreadsheet-db-mcp

A Model Context Protocol (MCP) server that lets AI agents (Claude Desktop, Cursor, Windsurf, …) work with entities managed by Hikoutei — a typed repository where local SQLite is the authority and Google Sheets is an asynchronous, human-facing projection.

Agents read and write SQLite through the same entity-lifecycle API an application would use. Sheet delivery happens in the background via Hikoutei's durable outbox, so an agent never fights the Sheets API quota, and a human editing the Sheet never gets silently overwritten: their edits surface as conflicts that need a human decision.

Status: v0.1.0 — published to npm as spreadsheet-db-mcp. Releases are tagged mcp-vX.Y.Z; the mcp-publish workflow patches the manifest, verifies a bare consumer install, and publishes with provenance.

Why this exists

Direct Sheets-API MCP servers hit three walls quickly: quota errors (429), schema-less cells (anything lands anywhere), and silent clobbering of concurrent human edits. Hikoutei's model avoids all three by design:

• Agent → SQLite. All reads/writes commit locally first; flush() is fast and offline.
• SQLite → Sheets, asynchronously. A durable outbox delivers effects with retry and stale-write protection; sessions can end mid-delivery and resume later.
• Human → Sheet → conflicts. Human edits in the User_Input projection are detected, recorded, and never auto-overwritten. v1 exposes them read-only via list_conflicts.

Install (once published)

npx -y spreadsheet-db-mcp

Configuration

The server needs (1) an entity declaration file and (2) the same environment variables the library uses.

1. hikoutei.config.json

Search order: --config <path> flag → HIKOUTEI_MCP_CONFIG env var → ./hikoutei.config.json in the working directory.

{
  "entities": [
    {
      "name": "users",
      "tableName": "users",
      "properties": {
        "id": { "type": "string", "primary": true },
        "name": { "type": "string" },
        "age": { "type": "number", "nullable": true },
        "createdAt": { "type": "date" }
      }
    }
  ]
}

• type is one of string, number, boolean, date (ISO 8601 strings cross the tool boundary).
• Exactly one property per entity must be primary: true; it is immutable after create.
• Names and table names must be SQL identifiers; tables reserved by Hikoutei or SQLite are rejected.

2. Environment

| Variable | Meaning | | --- | --- | | HIKOUTEI_SYNC_SPREADSHEET_URL | Spreadsheet URL; absent ⇒ local-only mode (no Google contact) | | GOOGLE_APPLICATION_CREDENTIALS | Service-account key file path (from hikoutei setup) | | HIKOUTEI_DB_PATH | SQLite path; default ./hikoutei.sqlite |

The server loads .env (or --env <path>) into gaps in the environment before startup, so the .env written by hikoutei setup can be reused as-is. Variables already set in the process always win.

Client setup

{
  "mcpServers": {
    "hikoutei": {
      "command": "npx",
      "args": ["-y", "spreadsheet-db-mcp"],
      "env": {
        "HIKOUTEI_SYNC_SPREADSHEET_URL": "https://docs.google.com/spreadsheets/d/<ID>/edit",
        "GOOGLE_APPLICATION_CREDENTIALS": "~/.gcp/hikoutei-service-account.json"
      }
    }
  }
}

For a local (unpublished) build, point command at node with <repo>/packages/mcp/dist/index.js as the argument and set the working directory where hikoutei.config.json lives.

Tools (v1)

| Tool | Input | Behavior | | --- | --- | --- | | list_entities | — | Entities with fields, types, primary keys | | create_record | entity, data | Validate → insert into SQLite → return stored row | | find_records | entity, where?, limit?, offset?, orderBy? | Filtered read; limit default 50, max 500 | | get_record | entity, id | Single read by primary key | | update_record | entity, id, data | Partial update; primary key immutable | | delete_record | entity, id | Delete by primary key | | get_sync_status | — | Mode, bound spreadsheet ID, outbox counts, unresolved conflict counts | | list_conflicts | limit? | Unresolved human-edit conflicts (read-only) |

where maps a field to a value (equality) or an operator object: eq, ne, gt, gte, lt, lte, in, nin, like.

Verify locally (before publishing)

npm run build          # root build builds ikisaki → root dist → this package
mkdir -p /tmp/spreadsheet-db-mcp-demo && cd /tmp/hikoutei-mcp-demo
# write hikoutei.config.json (see above; no env needed for local-only mode)
npx @modelcontextprotocol/inspector /path/to/Hikoutei/packages/mcp/dist/index.js

In the Inspector: connect → list tools → call list_entities, create_record, get_sync_status (expect {"mode": "local"}). No credentials are required for this smoke test.

Limitations (v1)

• No resolve_conflict yet. Conflicts are listed read-only; resolution tooling is planned.
• Entities are fixed per session. They come from hikoutei.config.json; defining entities at call time is not supported.
• Single server process per database. Running two spreadsheet-db-mcp processes against the same SQLite file concurrently is not supported.
• stdio transport only. No remote/OAuth server mode.
• get_sync_status / list_conflicts read the internal sync tables through the unstable hikoutei/internal/sync-status subpath, which is reserved for first-party tooling.

Development

npm run build -w spreadsheet-db-mcp        # after the root build
npm run typecheck:test               # includes packages/mcp
npm test                             # vitest includes packages/mcp/test

License: MIT (same as the repository).