YNAB MCP Server

Why This Exists

YNAB's budgeting philosophy works best when you interact with your budget frequently - but the app interface isn't designed for quick queries or bulk operations. "How much did I spend on groceries this month?" shouldn't require navigating three screens. "Categorize all my Amazon orders from this week" shouldn't be a manual, one-by-one process.

This server gives your AI assistant a safe interface to YNAB's API, turning natural language into budget review and, when explicitly enabled, budget operations. All monetary values are automatically converted between dollars and YNAB's internal milliunits format so the AI never has to think about it. Built on the official YNAB JavaScript SDK with direct API calls for the newest endpoints (category creation, category groups, money movements) that the SDK hasn't caught up with yet.

Quick Start

Install with MCPB

For Claude Desktop and other MCPB-compatible clients, download the local bundle from the v2.0.0 release:

Download ynab-mcp-server-2.0.0.mcpb

The bundle includes the YNAB favicon, production runtime dependencies, and setup prompts for your personal access token, optional default budget ID, and optional write-tool opt-in.

1. Get a YNAB Personal Access Token

Go to YNAB Developer Settings and create a new personal access token.

2. Configure your MCP client

Claude Desktop (claude_desktop_config.json):

{
  "mcpServers": {
    "ynab": {
      "command": "npx",
      "args": ["-y", "@oliverames/ynab-mcp-server"],
      "env": {
        "YNAB_API_TOKEN": "your-token-here"
      }
    }
  }
}

Claude Code (.mcp.json):

{
  "mcpServers": {
    "ynab": {
      "command": "npx",
      "args": ["-y", "@oliverames/ynab-mcp-server"],
      "env": {
        "YNAB_API_TOKEN": "your-token-here"
      }
    }
  }
}

Or install globally and point to the binary directly:

npm install -g @oliverames/ynab-mcp-server

{
  "mcpServers": {
    "ynab": {
      "command": "ynab-mcp-server",
      "env": {
        "YNAB_API_TOKEN": "your-token-here",
        "YNAB_BUDGET_ID": "optional-default-budget-id"
      }
    }
  }
}

That's it. Your AI can now talk to YNAB.

By default, the server registers read-only tools only. To expose tools that create, update, import, or delete YNAB data, add YNAB_ALLOW_WRITES=1 to the MCP server environment:

{
  "mcpServers": {
    "ynab": {
      "command": "npx",
      "args": ["-y", "@oliverames/ynab-mcp-server"],
      "env": {
        "YNAB_API_TOKEN": "your-token-here",
        "YNAB_ALLOW_WRITES": "1"
      }
    }
  }
}

What You Can Do

Features

Complete YNAB API v1.83 coverage with 45 tools when writes are enabled:

Design Decisions

• Read-only by default - write tools are not registered unless YNAB_ALLOW_WRITES=1 is set. Read tools are annotated with readOnlyHint: true; write tools are annotated with readOnlyHint: false, idempotency hints, and destructive hints for delete operations.

• Dollar amounts everywhere - inputs and outputs are in dollars (-12.34), never milliunits (-12340). Conversion is automatic and transparent.

• Smart budget resolution - set YNAB_BUDGET_ID for a default, or omit it to auto-resolve to your last-used budget. Every tool accepts an optional budgetId override.

• Pinned YNAB host - all HTTP requests are restricted to https://api.ynab.com, redirects are not followed, and API tokens are redacted from surfaced errors.

• Token fallback options - use YNAB_API_TOKEN, a small token file via YNAB_API_TOKEN_FILE, or a 1Password CLI reference via YNAB_OP_PATH.

• Split transactions - first-class support for subtransactions in create, read, and format operations.

• Bulk operations - create_transactions and update_transactions handle arrays in a single API call.

• Verified batch updates - update_transactions refetches every requested transaction after the bulk API call, retries mismatched fields once through update_transaction, and returns a verification block so approval counts cannot hide failed category writes.

• Fetch-then-merge updates - scheduled transaction updates (which use PUT semantics) automatically fetch the current state and merge your changes, so you only specify what changed.

• Fuzzy search - search_categories and search_payees do case-insensitive partial matching across all entries.

• Approval workflow with anomaly flags - review_unapproved groups transactions into "ready to approve" (categorized, split, or transfer) and "needs attention" (uncategorized), and attaches a flags array to each transaction surfacing anomalies: manually_entered (not bank-imported), match_broken (stale match reference), scheduled_transaction_realized, new_payee, no_prior_amount_match (novel amount for this payee), and category_drift:was_X (payee categorized differently in the prior 60 days). Group-level flags aggregate the union of all transaction flags.

• Nullable updates - update tools accept null for clearable fields (memo, payeeName, categoryId, flagColor) to distinguish "don't change" (omit) from "clear this field" (null).

• Target behavior support - category create/update tools expose goalNeedsWholeAmount for YNAB's "Set aside another" vs. "Refill up to" goal behavior.

• Delta request support - high-volume list tools accept lastKnowledgeOfServer and return server_knowledge when that parameter is provided.

• Debt account support - loan and debt accounts include debt_original_balance, debt_interest_rates, debt_minimum_payments, and debt_escrow_amounts with correct unit conversion (rates stay as percentages, payments convert from milliunits).

Tools Reference

Read tools are available by default. Tools that create, update, import, or delete YNAB data are marked as write tools and are registered only when YNAB_ALLOW_WRITES=1.

User & Budgets

Accounts

Supported account types: checking, savings, cash, creditCard, lineOfCredit, otherAsset, otherLiability, mortgage, autoLoan, studentLoan, personalLoan, medicalDebt, otherDebt

Categories & Category Groups

Payees

Payee Locations

Months

Money Movements

Transactions

Scheduled Transactions

Supported frequencies: never, daily, weekly, everyOtherWeek, twiceAMonth, every4Weeks, monthly, everyOtherMonth, every3Months, every4Months, twiceAYear, yearly, everyOtherYear

Convenience

Workflow Safety Notes

Write Tool Opt-In

The server starts in read-only mode. Write tools are not merely discouraged; they are absent from listTools unless YNAB_ALLOW_WRITES=1 is present when the MCP process starts. This mirrors the safer hosted-connector pattern: the default permission set can inspect budgets, transactions, categories, payees, months, and scheduled transactions, but it cannot mutate financial data.

If a client already has the process running, changing the environment is not enough. Restart the MCP server after setting or clearing YNAB_ALLOW_WRITES.

Batch Updates

When a batch operation categorizes and approves transactions at the same time, do not use review_unapproved counts as the only success check. Approved transactions leave the review queue even if a category write failed, so queue counts can hide approved-but-still-uncategorized transactions.

update_transactions now protects this path by refetching every requested transaction after the bulk API call and comparing the persisted fields with the requested fields. If anything differs, it retries that transaction once through update_transaction. The response includes:

{
  "verification": {
    "checked": 1,
    "retried": [],
    "failed": []
  }
}

Treat any failed entry as a real write failure and inspect the named transaction with get_transaction.

Credit Card Payment Transfers

If two unapproved transactions are clearly a credit card payment plus the matching checking-account outflow, convert them into a transfer before approval. Approving both sides as ordinary categorized transactions preserves the wrong structure and creates cleanup work.

Manual YNAB transfer fixes can replace one side of the pair with a new transaction ID. Read-only verification should not assume both original IDs survive. If one old ID returns resource_not_found, inspect recent activity in both involved accounts and verify the pair by transfer_transaction_id cross-links.

Environment Variables

*YNAB_API_TOKEN is required unless YNAB_API_TOKEN_FILE or YNAB_OP_PATH is set.

1Password Integration

If you store your YNAB token in 1Password CLI, set YNAB_OP_PATH to your secret reference and omit YNAB_API_TOKEN:

{
  "mcpServers": {
    "ynab": {
      "command": "npx",
      "args": ["-y", "@oliverames/ynab-mcp-server"],
      "env": {
        "YNAB_OP_PATH": "op://Personal/YNAB API Token/credential"
      }
    }
  }
}

The fallback adds ~1-2s to startup and is silently skipped if op is unavailable or the item is not found.

Amount Handling

All amounts in tool inputs and outputs are in dollars (e.g., -12.34 for a $12.34 outflow). The server converts to/from YNAB's internal milliunits format automatically.

Rate Limiting

The YNAB API allows 200 requests per hour per access token, enforced on a rolling window. This server applies a client-side limiter at 190 requests per hour with a burst of 10 by default. Each tool call typically uses one API request, except tools that deliberately verify or merge writes (update_transactions, update_scheduled_transaction) which perform additional reads.

Set YNAB_RATE_LIMIT_PER_HOUR=0 only for controlled local tests or smoke checks where you know you will stay under YNAB's API limit.

Architecture

┌─────────────────────┐     ┌──────────────────┐     ┌──────────────┐
│  AI Assistant       │────▶│  YNAB MCP Server │────▶│  YNAB API    │
│  (Claude, GPT, etc) │◀────│  (this package)  │◀────│  api.ynab.com│
└─────────────────────┘     └──────────────────┘     └──────────────┘
         MCP                    stdio transport           HTTPS/REST

• Transport: stdio (standard MCP server pattern)

• Auth: Bearer token via YNAB_API_TOKEN, YNAB_API_TOKEN_FILE, or YNAB_OP_PATH

• SDK: Official ynab v2.5+ for core endpoints, direct fetch for newer API features

• Safety: read-only default, explicit write opt-in, host-pinned HTTPS requests to api.ynab.com, no redirect following, redacted token errors

• Validation: All parameters validated with Zod schemas

• Error handling: API errors are caught, formatted, and returned as MCP error responses with detail messages

For a hosted OAuth connector design, see docs/hosted-oauth-connector.md.

Testing

The integration test suite runs against a live YNAB budget. Most write tests create temporary transactions and delete or restore them, but category and category group creation is not reversible through the public API and is skipped unless explicitly enabled.

YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id npm test

Use YNAB_TEST_BUDGET_ID to target a dedicated test budget without changing your server default. To include category and category group creation coverage, run with YNAB_RUN_NONREVERSIBLE_TESTS=1.

Tests cover all tool categories: reads, reversible writes, bulk operations, search, split transactions, scheduled transaction CRUD with fetch-then-merge verification, money movements, and payee locations.

MCP Smoke Tests

Use the smoke tests when you need to prove the server is reachable over stdio without reconstructing a custom MCP client. These commands use the official MCP SDK client, the same transport shape used by normal MCP hosts, and require YNAB_API_TOKEN because this server validates credentials at startup.

YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id npm run smoke:list-tools
YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id npm run smoke:review-unapproved
YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id YNAB_ALLOW_WRITES=1 npm run smoke:batch-verify

To test the package currently published to npm instead of the local checkout:

YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id npm run smoke:list-tools -- --published
YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id npm run smoke:review-unapproved -- --published
YNAB_API_TOKEN=your-token YNAB_BUDGET_ID=your-budget-id YNAB_ALLOW_WRITES=1 npm run smoke:batch-verify -- --published

smoke:list-tools verifies that high-value read tools such as review_unapproved, get_transactions, search_categories, and search_payees are present. When YNAB_ALLOW_WRITES=1 is set, it also verifies update_transactions. smoke:review-unapproved calls review_unapproved with summary: true and prints only aggregate counts. smoke:batch-verify creates a temporary transaction, uses update_transactions to categorize and approve it in one call, refetches it through the MCP server, and deletes it afterward.

Development

git clone https://github.com/oliverames/ynab-mcp-server.git
cd ynab-mcp-server
npm install
YNAB_API_TOKEN=your-token npm start

Dependencies

• @modelcontextprotocol/sdk - MCP server framework

• ynab - Official YNAB JavaScript client

Zero additional dependencies. No build step. Pure ESM.

Release Checks

Before publishing, run:

npm run release:check
npm run build:mcpb
npm pack --dry-run

After publishing, run npm run release:check:registry to verify the npm latest dist-tag, repo metadata, README release links, and MCPB artifact references all agree on the same version.

License

MIT