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Zach Gollwitzer edited this page May 10, 2024 · 11 revisions

What is the broad vision?

We are building a "COSS Personal Finance OS" (commercial, open-source personal finance operating system)

What does this mean?

We're hard at work to figure this out, but here's a "quickstart":

  • Personal finance tools that grow with your life circumstances
  • A "self-service" toolbox to help you make better decisions about your money

Think of it in terms of "Maybe Core" and "Maybe Apps":

  • Core - the "building blocks" of personal finance
    • Sign up individually and add your family
    • Add your accounts (checking, savings, credit card, loans, equity, crypto, etc.)
    • Manage your transactions (rules engine, quick search, categorization, notes, etc.)
  • Apps - only choose what you need at your current stage of life
    • Insights and Reporting
      • Net worth
      • Income and expenses by category, tags, accounts, etc.
      • Key ratios (debt/income, runway, etc.)
    • Budgeting
    • Goal setting
    • Retirement planning
    • Investment tracking
    • TBD...

What is "Maybe Core"?

We spent 2 years building Maybe 1.0. During that time, our team worked through a lot of engineering decisions around how to build a personal finance app.

Some of these decisions were good. Some were not. And some are no longer relevant to an open-source codebase.

The goal of this section is to help YOU (a capable Rails dev who probably knows a bit about personal finance as well) get a quick glance of what "Maybe Core" represents and where the first iteration of this is headed.

Moving from closed-source to open-source changes our assumptions and feature set. Here are some big ideas to keep in mind.

Core Views

Maybe "Core" is largely a backend concern, so the views required are minimal:

  • Dashboard
    • /
    • Provide a historical net worth graph
    • Provide basic insights for user
  • Accounts
    • /accounts
    • Allows user to see all accounts and do account-related CRUD actions
  • Account
    • /account/:id
    • Shows historical balance graph of individual account
    • Uses delegated types pattern to show "type-specific" views (i.e. a LoanAccount might show data about the loan such as interest rate, remaining principal balance, etc.)
  • Transactions
    • /transactions
    • Provides a "command center" for transactions across all accounts (explained in later section—search, filtering, sorting, pagination, rules, etc.)

Core Concepts

Concept #1: Get to 100% Accuracy with a "Demo User"

In Maybe 1.0, we placed a large focus on syncing user account data from data providers such as Plaid and Finicity.

With open-source, it will be the reverse. In our opinion, this is an advantage. In Maybe 1.0, we spent countless hours fixing data provider bugs and this got in the way of focusing on what truly matters—100% calculation accuracy.

The great news with finance is there is always a right answer. A calculation can be either be:

  • Correct
  • Wrong because of bad math/programming (in our control)
  • Wrong because of bad data (out of our control)

And when we have to aggregate a user's "net worth" into a single view, if there is anything wrong in the underlying calculations or data, the view is wrong.

In personal finance, wealth is not the only things that compounds exponentionally—calculation mistakes do too.

With this OSS version of the app, our primary goal is twofold:

  1. Create a rock-solid "demo user", which serves multiple purposes:
    • Allows new users to demo the product easily
    • Gives engineers clean test data to work with (for test suites, views, etc.)
    • Gives engineers confidence that we have the "right answer" (without tracking down the source of "bad data")
  2. Get the app to calculate everything with 100% accuracy for the demo account

Once we have a rock-solid "core" that can handle manual accounts, layering in data from external providers will be much easier.

Concept #2: "Self Service" Philosophy

Moving forward, the app will not deal with "advising". This was something we did in Maybe 1.0 that required a lot of overhead in terms of both compliance and costs.

In Maybe 2.0, we should be thinking in terms of a "self-service" model.

It will be much more of a "here's your data presented in several different ways so you can make good choices".

Things to consider here:

  • Giving user option to include/exclude "apps" (i.e. "grab what apps you need for your current stage of life")
  • Building an editable "rules engine" for classifying transactions

Concept #3: Dealing with Money (Globally this time)

With an OSS community, we're better equipped to tackle global currency concerns. In Maybe 1.0, everything was centered around USD.

This time around, we'll support global accounts and currencies.

Since we didn't implement this in 1.0, we'll need to build it fresh. Here are some things to consider:

Storing Monetary Values

You can't have "10 monies". 10 USD is very different than 10 CAD. To determine value of money, we need to store:

  • amount - stored as a Decimal(19,4)
  • currency - the ISO currency code

By having both pieces of information, we can easily convert values from one currency to another and support a multi-currency app.

Signage of Money

There are two important conventions used in the Maybe app:

  • Account Balance Convention
    • For asset accounts
      • A positive balance for an asset account means "I have money"
      • A negative balance for an asset account means "I've overdrafted (and owe) money"
    • For liability accounts
      • A positive balance for a liability account (i.e. credit card) means "I owe money" (credit balance)
      • A negative balance for a liability account (i.e. credit card) means "I've overpaid my credit and the bank owes me money"
  • Transaction Amount Convention
    • A negative transaction amount represents an inflow to the account
    • A positive transaction amount represents an outflow from the account

These conventions are in line with popular data providers such as Plaid (see account and transaction docs)

Formatting Money in the UI

A "default currency" should likely be set at the Family level. An obvious default here would be USD.

For something like a net-worth graph where there could be transactions with multiple currency types, we'll need a way to determine what "default" currency to show the graph in.

For something like a transaction, the formatting is simpler because we just use what's stored in the DB for that individual transaction.

Concept #4: Transactions "Command Center"

Whether it's a basic credit card transaction for your Chipotle meal or a more complex brokerage transaction with qty, shares, price, cusip, the concept of a "Transaction" is the basic "building block" of a personal finance app.

Especially since we're starting out "100% manual", users will need a "command center" for viewing and managing transactions across accounts.

This includes but is not limited to things like:

  • Searching (full text search)
  • Sorting
  • Filtering (view “All”, “by account”, “by tag”, “by category”, “by date”, etc.)
  • CRUD operations (single or bulk)
  • Transaction Import/Exports
  • Customizable "Rules Engine" for classifying transactions
    • Reviewing “auto classified” transactions (once 3rd party data is integrated)

Concept #5: Charts (long-term)

Having a standardized and composable charts module will be a long-term priority.

Maybe 1.0 was known for having clean and interactive charts to view historical data. We previously used Visx (a React library on top of D3.js) which made this a bit easier.

Now that we're in Rails, a vanilla D3.js integration would be a great addition for building Maybe-branded, "standardized" charts.

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