Marten

A calm, modern personal finance app for one household. Connect your banks or import a spreadsheet, then see your accounts, spending, recurring bills, investments, credit scores, and a forecast of the years ahead in one place. Free, open source, no ads, no selling data, no tracking.

What Marten does

• Accounts — checking, savings, credit cards, loans, brokerage, and IRAs, with net worth over time.
• Transactions — search, categories, tags, notes, splits, receipts, merchant logos, and ordered rules that categorize new activity for you.
• Cash flow and reports — income against expenses, spending by category and merchant, and complete-period totals you can trust.
• Recurring — subscriptions and bills detected from your history, with statement due dates and optional reminders.
• Investments — holdings, allocation, cost basis, and activity for connected brokerage accounts.
• Forecast — retirement ages, annual travel, required savings, and near-term cash balances, with every assumption visible.
• Credit scores — a history you keep yourself from the free scores your card issuers and bureaus already give you.
• AI-assistant connections — let an assistant you already use read (and, with separate consent, edit) your finances through the browser or a remote MCP connection. Marten runs no model and needs no model API key.
• Spreadsheet import — Excel and CSV, including Monarch Money exports, with column matching, previews, and duplicate handling.

Every signed-in person gets a private workspace. There is no household sharing yet. Trading, automated financial advice, and tax filing are outside its scope.

Why it exists

I built Marten for my family. We wanted something modern and simple that did not cost about $100 a year the way Monarch Money does, and that did not mean typing every purchase into a spreadsheet. In the United States, bank data is not open: apps reach it through an aggregator such as Plaid, SimpleFIN or Lunch Flow, so Marten lets you choose one and keeps the rest free.

Two ways to use it

	Hosted Marten site	Self-hosted
Who runs it	Drew hosts a public instance at marten.money for anyone who wants an account	You, for your own household
Cost	Free. Bank connections use your own SimpleFIN Bridge or Lunch Flow subscription, paid to that provider	Free tiers of Convex and a static host; a domain if you want one; Plaid's free Trial, SimpleFIN or Lunch Flow
Bank provider	SimpleFIN Bridge or Lunch Flow. Plaid on the hosted site is reserved for the operator's family	Your choice: Plaid (your own free Trial credentials), SimpleFIN, Lunch Flow, or manual and spreadsheet only
Get started	Create an account at marten.money, or try the demo first	Follow the self-hosting guide

Either way you can start with manual accounts and spreadsheet imports and connect a bank later.

Bank providers compared

	Plaid	SimpleFIN Bridge	Manual and spreadsheets
Who pays	The deployment operator; free Trial, then pay-as-you-go	Each user, directly to SimpleFIN	Nobody
Who sets it up	The operator, once, with developer credentials	Each user, in their own SimpleFIN account	Nobody
Limit	10 institution logins per Trial, for the whole deployment, ever	Up to 25 institutions and 25 apps per subscription (SimpleFIN's advertised terms)	None
Data	Balances, transactions, credit statements and minimum payments, investment holdings and activity	Balances and posted transactions with merchant category codes; holdings are not imported yet	Whatever you enter or import
Freshness	Webhooks plus a six-hour catch-up sweep	Once a day, plus Import latest on demand	You
Best for	The operator's own household	Everyone else on a shared deployment, or a self-hoster who would rather not manage Plaid	Getting started, or accounts no provider covers

Details and sources: bank provider options, Plaid, SimpleFIN, Lunch Flow.

How Plaid's free Trial works

Plaid is the provider Marten integrates most deeply, and its free Trial is enough for a household if you understand one rule: the Trial allows 10 Production Items, created in total, ever.

• An Item is one login at one institution. A Chase login that exposes three credit cards and two bank accounts is one Item. Your Chase login and a family member's separate Chase login are two Items.
• Creating an Item spends a slot permanently. Disconnecting or removing the Item in Marten (or in Plaid's dashboard) does not give the slot back.
• Reconnecting an existing Item in update mode (Marten's Reconnect button) repairs the same Item and does not spend a new slot. Always reconnect rather than adding the institution again; some OAuth banks such as Chase and Schwab invalidate the old connection if the same login creates a second Item.
• The Trial includes the products Marten uses: Transactions, Liabilities (statement balances, minimum payments, due dates), and Investments.
• Sandbox is separate from the Trial: it is free, uses fictional institutions and data, and is what Marten's automated tests use. Sandbox connections do not consume Trial slots, but they never show real accounts.
• Eligibility and approval belong to Plaid. At the time of writing the Trial applied to US and Canadian teams created on or after April 15, 2026, required identity verification and Plaid's standard agreement, and was not approved automatically for every applicant. Pay-as-you-go pricing after the Trial is shown on your own Plaid account; Marten does not restate it.

To get credentials:

1. Sign up at dashboard.plaid.com. New teams start with Sandbox keys.
2. Apply for Production access; the free Trial is the plan you are approved into. OAuth institutions can take a while to become available after approval.
3. On your Convex deployment set PLAID_CLIENT_ID, PLAID_SECRET, and PLAID_ENV (sandbox while testing, production for real banks). Missing or invalid settings simply hide the Plaid button.
4. For OAuth banks (Chase, American Express, Schwab), register your site's HTTPS origin as an allowed redirect URI in Plaid's dashboard and set the same value as PLAID_REDIRECT_URI.
5. On a shared deployment, set PLAID_ALLOWED_EMAILS (comma-separated) so only those accounts see Plaid. Everyone else can use SimpleFIN or Lunch Flow and your Trial slots stay with your family.

Sources: bank provider options and Plaid integration.

How Lunch Flow works

Connect banks in your own Lunch Flow account. Create an API destination, enable its Account Access settings, then choose Add account → Continue with Lunch Flow in Marten. Paste the key and review the accounts, types, mappings and import start date. Marten imports USD balances, posted transactions and supported holdings daily. The subscription and coverage are set by Lunch Flow; the API does not supply transaction categories, merchant logos or credit-card statement fields. Setup and data limits.

How SimpleFIN works

SimpleFIN Bridge is a small consumer subscription that connects to your banks once and then shares balances and posted transactions with any app you approve. It works on the hosted site and on any self-hosted Marten, because each person brings their own subscription.

1. Subscribe at SimpleFIN Bridge (about $1.50 + tax per month or $15 + tax per year at the time of writing; SimpleFIN sets the price) and link your banks there.
2. In the bridge, create a new app connection and copy the setup token.
3. In Marten, open Add account → Continue with SimpleFIN (or Settings → Bank connections), paste the token, then review the accounts: confirm each one's type, map it to an existing account if you are switching providers, and choose how far back to import.
4. The token is claimed exactly once, so Marten stores the resulting access URL (sealed when the operator has set CREDENTIALS_KEY) and never asks for the token again.
5. Marten imports once a day, or whenever you choose Import latest. Revoke the app in SimpleFIN Bridge at any time; Remove in Marten forgets the connection and keeps your history.

Marten never sees your bank password. Details: SimpleFIN connections.

Start here

For interface work, begin with Marten's design system. It records the current brand, themes, typography, components, layout, and motion rules. The Claude Design handoff carries the same system into external prototypes.

Document	Purpose
Self-hosting	Run your own Marten: Convex backend, auth keys, Netlify, environment variables, costs, and troubleshooting
Development guide	Install, configure authentication, run locally, and choose the right checks
Architecture	Source map, data flow, finance conventions, and change boundaries
Requirements	Product scope and acceptance criteria
Plaid integration	Trial and Item semantics, credentials, OAuth, sync invariants, and bank-data limitations
SimpleFIN connections	Per-user bridge tokens, reviewed import, daily catch-up, and data limits
Bank-provider options	Plaid's limits, SimpleFIN, and the research behind the provider choice
Authentication	Email sign-in, password recovery, delivery setup, and request limits
Importing spreadsheets	Excel/CSV columns, previews, duplicate handling, and account mapping
Forecast guide	Saved scenarios, travel, savings, cash runway, and model limitations
Investments	Holdings, valuation, cost-basis coverage, and investment sync
Agent access	Browser WebMCP, remote MCP, consent and assistant setup
Reminders	Opt-in browser and email notifications
Brand and category artwork	Offline logo catalog and illustrated category icons
Recurring schedules	Precise subscription matching and manual statement reminders
Forecasting research	Competitor evidence, user needs, and model requirements
Credit-score history & research	Provider access, free consumer sources, and practical import options
Verification record	Observed checks and remaining release work
Design system	Layout, typography, color, responsive behavior, and visual references
Contributing	How to run the app, which checks to run, and where documentation lives

Run locally

Use Node.js 22.12 or newer, as required by package.json, and the committed npm lockfile:

npm ci
npm run backend

In a second terminal:

npm run dev

The backend command starts the Convex development watcher and pushes backend changes to the selected development deployment; on a fresh clone it walks you through creating a free Convex project. The frontend command starts Vite at http://127.0.0.1:5173 when that port is available; use the URL printed by Vite.

The Convex CLI writes the ignored .env.local. The browser needs VITE_CONVEX_URL, which is a public endpoint rather than a secret. Authentication and Plaid setup are explained in the development guide.

Open /demo to explore a fictional household in an isolated browser tab. Profile → Open demo keeps an existing account signed in; Exit demo returns to the normal account or sign-in screen. Guest accounts cannot connect banks.

Checks

npm test
npm run typecheck
npm run lint
npm run build

Tests use Vitest, the edge runtime, and convex-test. They exercise isolated backend functions and shared finance/UI state logic. The Plaid tests mock provider responses; they do not contact banks or spend live Trial connections. Typecheck and build do not prove that sign-in, a browser interaction, or a bank connection works.

Formatting uses the installed Prettier configuration. Format files you change; generated code, dependencies, builds, and other workstreams should not be swept into a formatting edit. See development checks.

Deployment boundary

The React build goes to dist; Convex hosts the backend separately. Publishing the site is a separate release step that requires the chosen backend, final HTTPS origin, SPA fallback routing, authentication configuration, and Plaid OAuth settings to agree. The self-hosting guide walks through it on Netlify.

Keep signing keys, Plaid secrets, and CREDENTIALS_KEY in Convex deployment configuration. Never place them in browser VITE_* variables or tracked files. A working development deployment does not establish a public release or live bank consent. Track those outcomes separately in verification.md.

Feedback and support

• Bugs, feature requests, and questions go through GitHub issues. Pick the bug, feature request, or question template. The in-app Send feedback button opens the right template with your browser and device details already filled in.
• Source and updates live at github.com/dlev02/marten. Starring the repository is a nice way to say it is useful, and watching it is the easiest way to hear about releases.
• Donations are optional and never unlock anything. If Marten saves you a subscription and you want to say thanks: Ko-fi. GitHub Sponsors may be added later.

License and credit

Marten is free software under the GNU AGPL v3 or later, with one additional term (see NOTICE.md): every copy, fork, or hosted instance must keep visible credit to the original author — "Built on Marten by Drew" with a link to this repository — in the app and in its documentation. You can run it, change it, self-host it, and share it; changes must stay open under the same license, and people using a hosted copy must be able to get the source. Renaming it and dropping the credit is not allowed.