ynab-mcp-server

ynab-mcp-server

A Model Context Protocol (MCP) server for interacting with your YNAB plans at https://ynab.com

In order to have an AI interact with this tool, you will need to get your Personal Access Token from YNAB: https://api.ynab.com/#personal-access-tokens. When adding this MCP server to any client, you will need to provide your personal access token as YNAB_API_TOKEN. This token is never directly sent to the LLM. It is stored privately in an environment variable for use with the YNAB api.

A Model Context Protocol server that lets an AI assistant read and modify a YNAB plan.

The server talks to the YNAB API through the official ynab SDK. Your Personal Access Token lives in an environment variable and is never sent to the model.

It runs two ways from one codebase:

• Local (stdio) — a child process of Claude Code or Claude Desktop on your own machine. Simplest, but only works on that machine while it is running.
• Remote (Cloudflare Worker) — deployed behind GitHub sign-in and added to claude.ai as a custom connector, so it works from the web and the mobile app with your computer switched off. See DEPLOY.md.

Both entry points register the same tools from src/registry.ts, so a tool written once is available in both.

Other providers:

Setup

Get a Personal Access Token from https://api.ynab.com/#personal-access-tokens, then:

npm install
npm run build

Environment variables:

Local: Claude Desktop / Claude Code

{
  "mcpServers": {
    "ynab": {
      "command": "node",
      "args": ["/absolute/path/to/ynab-mcp-server/dist/index.js"],
      "env": {
        "YNAB_API_TOKEN": "your-token",
        "YNAB_PLAN_ID": "your-plan-id"
      }
    }
  }
}

Remote: phone and claude.ai

The stdio server above cannot be reached from a phone. To use these tools from claude.ai or the Claude mobile app, deploy src/worker/ to Cloudflare Workers and add it as a custom connector. DEPLOY.md has the full walk through; the shape of it:

1. Copy wrangler.example.jsonc to the git-ignored wrangler.jsonc, run npx wrangler login, then create the OAUTH_KV namespace
2. npm run deploy once to learn your *.workers.dev hostname
3. Create a GitHub OAuth app whose callback is https://<host>/callback
4. Use npx wrangler secret put for ALLOWED_GITHUB_LOGIN, YNAB_API_TOKEN, GITHUB_CLIENT_ID, GITHUB_CLIENT_SECRET, and TYPESAFE_API_KEY
5. Run npm run deploy again
6. Add https://<host>/mcp as a custom connector in claude.ai

The YNAB token stays a Worker secret and never reaches the client. GitHub sign-in controls who may connect to the remote Worker; the YNAB Personal Access Token controls which YNAB account it reaches. They answer different questions, and neither substitutes for the other. The Worker uses one server-wide YNAB token, so anyone admitted through the GitHub gate reaches the deployer's YNAB account, money, and every plan available to that token—not their own YNAB account. ynab_list_plans lists all of those plans, and a caller-supplied planId overrides the optional YNAB_PLAN_ID default. Any GitHub account other than ALLOWED_GITHUB_LOGIN is refused. This matters because the tool set can create and delete transactions—an unauthenticated endpoint would grant access to those plans to anyone who found the URL.

The Worker is not tied to Claude. Any MCP client that supports remote servers with OAuth can connect, for example Claude (claude.ai, desktop, and mobile), ChatGPT connectors, Claude Code, or the MCP Inspector. Because clients register themselves, every permitted sign-in shows an approval page naming the client and the exact address the grant will be sent to; approve only a sign-in you just started. To restrict which clients can connect at all, set ALLOWED_REDIRECT_URIS to their exact callback URIs (loopback redirects for local clients stay allowed). See Approving MCP clients for example callback URIs.

Why not YNAB OAuth?

YNAB OAuth is deliberately not supported. Its token exchange requires a client secret even with PKCE; an open-source package cannot ship a secret, so a local package cannot honestly implement the authorization-code flow (OAuth application requirements). The only secretless flow YNAB documents is the implicit grant, which expires in two hours with no refresh (OAuth application requirements). YNAB recommends a Personal Access Token for an individual accessing their own account (Personal Access Tokens).

Setting YNAB_READ_ONLY to "true" drops every write tool from the tool list, which is worth considering for a connector you will mostly use on a phone.

Tools

Plan-scoped tools take an optional planId that falls back to YNAB_PLAN_ID. Optional tool inputs may be null; the server treats null the same as omitting that input. All monetary values — in both directions — are plain currency amounts, never YNAB's milliunits; conversion happens in src/tools/money.ts.

Reading

Category suggestions (optional)

ynab_apply_category_suggestions is a separate write tool that is available without enabling the TypeSafe preview. Provide up to 25 explicit transaction_id, category_id, and expected_content_fingerprint rows. The tool refetches each transaction and rejects stale or ineligible changes; a retry whose category is already applied is a no-op. It supports validation-only dry runs and returns a pre-write undo manifest, but does not perform the undo. It never auto-applies suggestions, calls TypeSafe, or approves transactions.

ynab_suggest_categories is off by default. To expose it, set both an operator-owned TYPESAFE_API_KEY and YNAB_AI_CATEGORIZATION=true, then restart the server. The API key is read from the environment (or a Worker secret), never from a tool argument. Omit transactionIds, pass null, or pass an empty array to fetch unapproved transactions and retain only uncategorized rows; provide IDs to inspect only those transactions. In default mode, the tool checks every retained row for deterministic eligibility and then applies limit to the first eligible outflows in YNAB's returned order. Skipped rows do not consume the limit.

The tool is a dry-run preview: it never writes to YNAB, approves a transaction, or changes the behavior of ynab_update_transaction. It first handles exact facts in code—dropping deleted rows and handling approved or reconciled rows, YNAB balance adjustments, transfers, splits, inflows, existing categories, and hidden/internal categories. In default mode, transactions contains only the eligible rows inspected, transaction_count is that row count, and eligible_transaction_count reports all eligible rows available before the limit. The top-level skipped object reports total_count and a count plus transaction_ids for each reason: skipped_approved, skipped_reconciled, skipped_balance_adjustment, skipped_transfer, skipped_split, skipped_inflow, and skipped_already_categorized. With explicit transactionIds, every non-deleted fetched row remains an individual result, including rows carrying a skipped_* status; deleted rows are omitted. Payee history uses the latest 12 months, capped at 50 qualifying rows. When the payee has no qualifying rows with the same payee ID, history falls back to rows from payees with a similar name: after Unicode NFC normalization, lowercasing, and removing everything except letters and numbers, one name begins the other and the shorter is at least six characters, so a truncated bank payee such as "Better Bl" draws on "Better Blend" history. Each history summary reports match (payee, similar_payee_name, or null) and matched_payee_names. The deterministic history rule applies only when at least three exact-payee rows all use the same still-eligible category. Similar- name history always goes to the model as suggestive evidence and never bypasses it. Every other eligible row goes to TypeSafe's pinned jev-1.13.0 System One model in batches of ten. A disagreement between exact-payee history plurality and the model forces needs_review; similar-name disagreement is reported in the history summary but does not force review because a prefix match does not establish merchant identity. Every inspected eligible row includes a status, content fingerprint, proposed category, confidence, winning probability, up to three alternatives, and history summary. Applying a suggestion remains a separate, explicit human decision using ynab_apply_category_suggestions (or the general ynab_update_transaction tool).

Enabling this feature sends the transaction's display payee, imported/original payee, memo, amount, date, and account name/type/on-budget status, plus visible category group and category names, to TypeSafe as a third-party processor. For similar-name matches only, it also sends the matched payee names and per-category key, group, name, and count. It does not send YNAB UUIDs, balances, goals, approval/cleared state, or raw transaction history. TypeSafe's published Jev 1.13 price at the time of this release is $0.042 per million input tokens; output tokens are free. The tool returns preflight estimates, actual token usage, and projected cost on each run and refuses requests over its per-call token/cost ceilings. Pricing and provider limits can change; check https://docs.typesafe.ai/models.

The prototype is intentionally narrow and not default-on. Its supporting 98.3% exact-label, 98.9% top-three, and 60/60 expected-abstention results came from 40 synthetic, single-evaluator fixtures—not a production accuracy claim.

Reporting

Splits are counted through their subtransactions and transfers between your own accounts are excluded, so these report spending rather than money movement.

Writing

Names instead of IDs

ynab_create_transaction accepts accountName and categoryName and matches them loosely against the plan, so "ally checking" finds Ally Checking. Closed accounts and hidden categories are never matched. If a name is ambiguous or unrecognised the call fails and names the near misses rather than guessing, and successful calls echo back matchedAccount / matchedCategory so a wrong guess is visible.

Split transactions

ynab_create_transaction and ynab_update_transaction split a transaction across categories when given subtransactions: two or more entries of { amount, category_name, payee_name, memo }, the same shape ynab_get_transactions returns for a split. Amounts are in dollars and must add up to the transaction amount exactly (on update, the new amount if given, otherwise the current one); categories go on the splits, not on the parent. Split category names are matched like categoryName and echoed back as matchedSplitCategories.

YNAB cannot change the splits of a transaction that is already split, so ynab_update_transaction refuses rather than silently dropping the change. Delete and recreate the transaction to re-split it.

Writes that can half-succeed

YNAB has no endpoint for moving money between categories, so ynab_move_money rewrites both categories' budgeted amounts in two calls. It takes from the source first, so a failure in between leaves the money in Ready to Assign rather than double-counted. When that happens the response sets partial: true and carries a recovery line with the original amount to restore. ynab_auto_assign behaves the same way: on failure it reports which categories were already funded and which were left alone.

Tools never throw at the protocol level. Failures come back as an MCP error result (isError: true) with { "success": false, "error": "..." } in the text content, so a failed write is never mistaken for a successful one.

Tool annotations

Every tool advertises MCP annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint) alongside its schema. Reading tools are readOnlyHint: true; among the writing tools, only ynab_delete_transaction sets destructiveHint: true. A client may use these hints to decide which calls need a confirmation prompt.

cleared and flagColor

ynab_create_transaction and ynab_update_transaction accept cleared as one of cleared, uncleared, or reconciled, and flagColor as one of red, orange, yellow, green, blue, purple, or "" to clear an existing flag.

Development

npm run watch          # rebuild on change
npm test               # vitest (watch mode)
npm run test:run       # vitest, single run
npm run test:coverage  # coverage report
npm run typecheck      # typecheck both the node and Worker targets
npm run debug          # build, then open the MCP inspector
npm run dev:worker     # run the Worker locally with wrangler
npm run deploy         # deploy the Worker to Cloudflare

dist/ is a build artifact and is not tracked in git; npm run build regenerates it.

Releasing

Bump the version in package.json and update CHANGELOG.md, then merge to main and create a GitHub release tagged in the existing 0.2.0 style (without a v prefix). The workflow stages that release with npm; it does not make the package public. The maintainer must run npm stage list, review it, and run npm stage approve with 2FA to promote it live. Configure a Trusted Publisher on npmjs.com for ynab-mcp-server, pointing at GitHub repository calebl/ynab-mcp-server and the exact workflow filename .github/workflows/publish.yml (the filename must match exactly); under Allowed actions select only npm stage publish.

Adding a tool

Each tool is a self-contained module in src/tools/ exporting name, description, inputSchema (a Zod shape) and execute(input, api). See CLAUDE.md for the full template, then add the module to the tools array in src/registry.ts and write a test in src/tests/. Registering it there serves it from both the stdio server and the Worker; mark writes: true if the tool changes data, which is what YNAB_READ_ONLY filters on.

Useful references:

• YNAB SDK types: node_modules/ynab/dist/index.d.ts
• YNAB OpenAPI spec: https://api.ynab.com/papi/open_api_spec.yaml

Contributing

Pull requests targeting main must be raised through no-mistakes. Install it, run no-mistakes init, commit your changes, and push with git push no-mistakes so the review/test pipeline can open a compliant PR. See the no-mistakes quick start for setup.

Compatibility

ynab_list_budgets and ynab_budget_summary remain accepted aliases for the plan-named tools. budgetId and YNAB_BUDGET_ID are deprecated but still accepted; there is no removal date. Use planId and YNAB_PLAN_ID for new integrations.

License

See LICENSE.