YNAB MCP Server

Run YNAB through Claude Code, Codex, Hermes, Antigravity, or any stdio MCP host without a marketplace plugin. This server gives AI assistants a local, rate-aware YNAB API layer that is read-only by default, speaks in dollars instead of milliunits, and exposes write tools only after explicit opt-in.

Why This Exists

YNAB's budgeting philosophy works best when you interact with your budget frequently, but the app interface is not designed for quick questions or careful bulk cleanup. "How much did I spend on groceries this month?" should not require navigating three screens. "Categorize all my Amazon orders from this week" should not become a manual, one-by-one review.

This server gives your AI assistant a safe local interface to YNAB's API, turning natural language into structured budget review and, when explicitly enabled, budget operations. It is designed for real budgeting work: finding overspending, reviewing unapproved transactions, checking category drift, investigating recurring payments, and making verified batch updates without giving the assistant broader access than it needs.

All monetary values are automatically converted between dollars and YNAB's internal milliunits format so the AI never has to think about it. The server uses the official YNAB JavaScript SDK where it fits, plus direct API calls for newer endpoints and query parameters that the SDK has not caught up with yet.

Related MCP server: YNAB Assistant

Quick Start

This package stands on its own as a stdio MCP server. You can install it from this repo as a standalone Claude Code, Codex, Hermes, or Antigravity plugin, or register the npm package directly and let your MCP client launch it on demand. You do not need the older ames-connectors marketplace for YNAB.

This is the local, owner-run package. It uses a personal access token because it is intended for a YNAB account owner running the MCP server for that same account. A public connector for other YNAB users should be reviewed as an OAuth application and should follow the hosted pattern in docs/hosted-oauth-connector.md.

Install as a Plugin

Install the standalone marketplace from this repository:

/plugin marketplace add oliverames/ynab-mcp-server
/plugin install ynab-mcp-server@ynab-mcp-server

Install the same marketplace in Codex:

codex plugin marketplace add oliverames/ynab-mcp-server
codex plugin add ynab-mcp-server@ynab-mcp-server

The plugin starts @oliverames/mcp-server-for-ynab@latest and preserves the prior ames-ynab connector behavior by setting YNAB_ALLOW_WRITES=1. Direct MCP registration remains read-only unless you explicitly enable writes.

Other Plugin Hosts

The repository also carries host-specific marketplace and plugin manifests for Hermes and Antigravity:

1. Get a YNAB Personal Access Token

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

Do not ask another YNAB user for a personal access token. If you are building a public connector for accounts you do not own, use YNAB OAuth instead.

Credential lookup order:

1. Values passed directly to the MCP process, such as YNAB_API_TOKEN.

2. The detected host's plaintext settings: Codex reads ~/.codex/config.toml, first [shell_environment_policy.set], then [mcp_servers.ynab.env]; Claude Code reads ~/.claude/settings.json under top-level env.

3. The other supported agent config as a fallback, useful when a token is already stored locally but the launcher did not inject it.

4. YNAB_API_TOKEN_FILE, if configured in any of the sources above.

5. YNAB_OP_PATH, if configured in any of the sources above and the op CLI is available.

If no token is found, ynab_auth_status returns a structured setup guide. Agents should first ask whether the user already has the YNAB token in a password manager such as 1Password. If yes, ask permission before configuring YNAB_OP_PATH; otherwise ask the user to add YNAB_API_TOKEN to the correct Codex or Claude config file and restart the MCP server.

2. Install in Claude Code

Use user scope if you want the server available in all Claude Code projects:

claude mcp add ynab --scope user \
  -e YNAB_API_TOKEN=your-token-here \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

Add a default budget ID if you do not want tools to use YNAB's last-used budget:

claude mcp add ynab --scope user \
  -e YNAB_API_TOKEN=your-token-here \
  -e YNAB_BUDGET_ID=optional-default-budget-id \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

Use --scope project instead of --scope user if you want Claude Code to write a project-local .mcp.json.

If ~/.claude/settings.json already contains env.YNAB_API_TOKEN, you may omit -e YNAB_API_TOKEN=...; the server will read the Claude setting as a fallback if the launcher does not inject it.

Verify Claude Code can see the server:

claude mcp get ynab

If Claude Code reports that ynab already exists, remove the old entry and run the add command again:

claude mcp remove ynab

3. Install in Codex

Register the same npm package directly with Codex:

codex mcp add ynab \
  --env YNAB_API_TOKEN=your-token-here \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

With a default budget ID:

codex mcp add ynab \
  --env YNAB_API_TOKEN=your-token-here \
  --env YNAB_BUDGET_ID=optional-default-budget-id \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

If ~/.codex/config.toml already contains YNAB_API_TOKEN under [shell_environment_policy.set] or [mcp_servers.ynab.env], you may omit --env YNAB_API_TOKEN=...; the server will read the Codex setting as a fallback if the launcher does not inject it.

Verify Codex can see the server:

codex mcp get ynab

If Codex reports that ynab already exists, remove the old entry and run the add command again:

codex mcp remove ynab

4. Enable Write Tools (Optional)

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 when you register the server:

claude mcp add ynab --scope user \
  -e YNAB_API_TOKEN=your-token-here \
  -e YNAB_ALLOW_WRITES=1 \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

codex mcp add ynab \
  --env YNAB_API_TOKEN=your-token-here \
  --env YNAB_ALLOW_WRITES=1 \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

Destructive direct tools, bulk-filter write tools such as approve_transactions and reassign_payee_transactions, and the generic ynab_write_tool_execute helper also require confirmed: true in the tool input after explicit user confirmation. For extra protection, pass expectedMatchedCount when using bulk-filter writes.

Manual JSON Config

Claude Desktop (claude_desktop_config.json):

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

Generic MCP client:

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

If you prefer a global install, point your MCP client at the package binary directly:

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

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

1Password Token Lookup (Optional)

If your token is stored in 1Password, set YNAB_OP_PATH instead of YNAB_API_TOKEN. The op CLI must be installed and authenticated in the environment that launches the MCP server.

claude mcp add ynab --scope user \
  -e YNAB_OP_PATH="op://Personal/YNAB API Token/credential" \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

codex mcp add ynab \
  --env 'YNAB_OP_PATH=op://Personal/YNAB API Token/credential' \
  -- npx -y @oliverames/mcp-server-for-ynab@latest

Local Smoke Test

From this repo, you can verify the published npm package without changing any MCP client config:

YNAB_API_TOKEN=your-token-here npm run smoke:review-unapproved -- --published

What You Can Do

Features

YNAB API v1.85 coverage with 47 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.

• Explicit destructive confirmation - delete tools require confirmed: true in their input after user confirmation. Bulk-filter writes also require confirmed: true, and support expectedMatchedCount when the current match count needs to be locked before mutation.

• 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.

• Agent-aware token fallback - use direct process env, Codex ~/.codex/config.toml, Claude ~/.claude/settings.json, 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.

• Current transaction filters - transaction list tools support sinceDate, untilDate, type filters, resource filters, and delta requests. YNAB defaults omitted sinceDate to one year ago, so pass an explicit older date when you need older history.

• 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. Bulk approval requires confirmed: true.

• 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.

High-impact writes require confirmation in the tool input, not only in surrounding chat. This applies to direct delete tools, approve_transactions, reassign_payee_transactions, and ynab_write_tool_execute:

{
  "confirmed": true,
  "expectedMatchedCount": 3,
  "payeeId": "payee-id-to-approve"
}

If expectedMatchedCount is provided and the current match count differs, the tool returns an error before mutating any transactions.

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. These values may come from direct process env, Codex config, or Claude settings.

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/mcp-server-for-ynab"],
      "env": {
        "YNAB_OP_PATH": "op://Personal/YNAB API Token/credential"
      }
    }
  }
}

The fallback adds ~1-2s to startup. If op is unavailable or the item is not found, ynab_auth_status reports the lookup problem and returns setup guidance instead of letting a normal YNAB tool fail with a generic unauthorized error. If no token source is configured, the setup guide tells the calling agent to ask whether you have a token in 1Password or another password manager, request permission before editing agent config, and otherwise ask you to add YNAB_API_TOKEN to the appropriate Codex or Claude settings file.

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

• Transport: stdio (standard MCP server pattern)

• Auth: Bearer token via process env, Codex or Claude agent config, YNAB_API_TOKEN_FILE, or YNAB_OP_PATH for local owner-run use

• SDK: Official ynab v4.1+ for core endpoints, direct fetch for newer API features and v1.85 transaction filters

• Safety: read-only default, explicit write opt-in, confirmation gates for destructive and bulk-filter writes, 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. For data handling details for this local package, see docs/privacy.md.

Public Listing Readiness

This repository is production-ready as a local owner-run stdio MCP package. For a public "Works with YNAB" style listing, confirm the listing scope with YNAB first:

• If YNAB accepts a local owner-run package, submit this package with the published privacy policy, non-affiliation language, read-only default, write opt-in, confirmation gates, and test evidence.

• If YNAB expects an OAuth application for public distribution, use docs/hosted-oauth-connector.md as the implementation checklist before submission.

• Keep public display names in the "for YNAB" pattern and avoid names that imply sponsorship or official support.

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. smoke:list-tools can run without a live token to verify discovery, but live read and write smokes need a token from process env, supported Codex or Claude settings, YNAB_API_TOKEN_FILE, or YNAB_OP_PATH.

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 sync:plugin
npm run release:check
npm pack --dry-run

After publishing, run npm run release:check:registry to verify the npm latest dist-tag and repo metadata agree on the same version. npm run build:mcpb remains available for an explicit local bundle, but the normal install path is direct MCP registration through npm.

Privacy and Non-Affiliation

See docs/privacy.md for this connector's data handling, deletion, and token-use details.

This connector is not affiliated, associated, or in any way officially connected with YNAB or any of its subsidiaries or affiliates. The official YNAB website can be found at https://www.ynab.com.

The names YNAB and You Need A Budget, as well as related names, trade names, marks, trademarks, emblems, and images are registered trademarks of YNAB.

License

MIT